I am not going to pretend that I know all about GTL's settings, but generally in other programs you change a setting like this so that the server and client can optimize the data they are sending so it does not overwhelm your connection and make the game unplayable.
Generally you set your client to match the sort of connection that you have but going lower should not cause issues. however, idk about GTL specifically so I might just be full of crap here. *shrug* you can try testing with different selections and see what happens.