Sure. An API node is just a server that connects to the Bitshares blockchain and provides all the data necessary to run a wallet. The users wallet, either through a website or by an app on their computer/phone sends out requests for information like market data, account balances, history etc. as well as requests for placing orders and sending funds. The API node handles these request so the user doesn't need to run a full server themselves.

Bitshares users benefit by having another location to connect to. For a while the only servers you could find were in Germany or China. These few servers were getting over worked and because they were halfway around the world for US users the latency was often so high that the wallet became hard to use or unstable.

Having more nodes means spreading the workload around as well as offering closer connections for lower latency which should provide a more consistent and enjoyable experience.