Probably the best known deserter in the Revolutionary War was Benedict Arnold. Because he took valuable military information with him (sent it ahead, actually) he is more often called a ‘traitor’ than a deserter, but he did quit his side in the fighting without leave. He deserted. Another man you are less likely to have heard of was Daniel McGirt. He quit his militia unit to stop an officer from appropriating his horse, and then he stole other horses. Both of these men went over to the other side and served the enemy. Arnold tore up Connecticut and Virginia ports and things awaiting export during the war's second half. McGirt was a superior horseman and had ridden the interior of Georgia and northern Florida, so he was able to lead Tory militiamen to distant plantations to steal horses and slaves.
Not every deserter went over to the other side. Some, mostly Americans, didn’t. What a man did after he left his unit depended on his situation. Why had he run away?
Surprisingly few men ran away because of a fear of getting shot and possibly killed. Physical cowardice led to few desertions. The cowards hadn’t enlisted, in the first place. Even if an American militiaman changed his mind after signing up, he likely wouldn’t desert. He was serving with his neighbors and friends. If he ran away, how would he face them when they came home? A deserter not only had to live down what he had done, he had to get family and friends to shield him from outsiders (in case someone came looking for him) or he had to entirely give up his previous life and go somewhere else. Did he have a wife and children to take with him? Some men who deserted did move west of the Allegheny Mountains to start life over. Others went to an area in Vermont.
An American soldier ran away because he thought military punishments given out were too severe. Small infractions could get up to fifty lashes. Some court sentences were for two hundred lashes.
An American soldier ran away because the officer who commanded his unit had been replaced by a Continental Army officer. The officer who had gotten him to enlist for six months to a year by promising to be fair with him had given way to an arrogant swine who treated enlisted men like dogs.
An American soldier ran away to do the spring planting or fall harvesting on his farm. His wife and kids couldn’t do it by themselves and his neighbors had their own fields to take care of. His family might starve over the winter and certainly wouldn’t have enough extra to barter for things they needed. (He more often than not returned to duty after his chores were done.)
An American soldier ran away to enlist in another militia unit. When he signed up, he had been promised one or several month’s pay as a bonus. As soon as he collected it, he ran off to sign up for another bonus from some other outfit. One man who did this seven times was caught and hung.
As many as one out of four American soldiers during the Revolutionary War deserted. This happened more in the first years, 1775-77. By 1778, men were signing up for longer enlistments and getting better training. The increase in their morale led to fewer desertions.
Both soldiers in the Royal Army and mercenary Hessian units deserted, but not in the numbers that the Americans did. A few hundred men ran away from the Royal Army every year. If he was English, it was likely he wanted to escape the army because of its rigidity of structure and discipline, its treating him as if it did not matter whether he lived or died, or its giving rewards to officers for valorous action, but not to him. He might have done something wrong and was due for three or five hundred lashes. English military justice was draconian. It destroyed the guilty and instilled fear into men who were forced to watch.
An English deserter was unlikely to join the Continental Army. If he had a skill (also unlikely) he went to a place where he could practice it and not meet anyone from the Royal Army who might know him. He otherwise hired himself out to a farmer for a season or indentured himself to a craftsman. He might also become a petty thief to support himself, which he might have done in England before becoming a soldier.
Hessian mercenaries deserted so they wouldn't be sent home after the war or be sent to another one to fight for the English. But do you suppose many of them spoke the local language? That might have had something to do with their deserting in only small numbers (up until 1781). An English soldier could change his clothes and be thought an American by another Englishmen, if the latter had never met the former. (Americans would quickly catch onto his not being an American.) A Hessian would give himself away every time he tried to make his wants known.
One way a Hessian could desert and get along was to enlist in the Continental Army. The Americans were desperate for bodies. They didn’t turn down foreigners just because of a simple language problem. If he was shouted at enough times and hit in the head enough times, he would learn. By 1780, there were units in the French Army fighting in the war that were comprised entirely of Hessian deserters. (A few thousand deserted in the last two years of the war. Most of them went north to Canada and farmed.)
The Continental Congress tried to encourage Royal Army soldiers and Hessian mercenaries to desert. Within months of the Royal Army and Hessians landing on Long Island in 1776 and crossing to New York, paper broadsides were printed and mysteriously distributed among the enemy ranks. On 29 April 1778, the Congress promised to give fifty acres to any mercenary who deserted and made his way to American authorities. An officer who deserted and brought forty of his men with him was to get eight hundred acres and a dozen farm animals. These men would not have to fight on the American side in the war, but could stop fighting and become civilians.
The ground forces were not the only military units to suffer desertions. The Continental Navy and the Royal Navy both had the problem. Most sailors on both sides deserted for the same reason: Being a merchant sailor paid a lot more than being a navy sailor. An added bonus was that a man was far less likely to become involved in a naval battle (where most men who were wounded later died of their wounds).