Because block trades don't happen on the open market the large size of the trades doesn't create volatility in the stock being traded. These types of purchase orders are made by institutions purchasing a large number of a security and retail investors can find watching for block trades useful because it indicates "smart money" has entered into a position. The BABA Technologies Trades: Below is a look at the notable alerts, courtesy of Benzinga Pro : BABA Price Action: Alibaba closed Friday's session down 1.61% at $157.96.