For me it is very distracting and sometimes I lose my thought and my concentration on gambling because I have looks at the chat. There should be another place to chat with other people that should not be visible when gambling.
There is always a way to hide/minimize the chat, so it wont affect your concentration. Chat room is used to communicate between gamblers while they are gambling. You do not need to look at the chat if you want, no gambling site forces you to look at the chat box. Regarding trolls or spams, most sites has their own chat moderators to avoid such things.