It's sometimes useful to use the quote feature when there is a busy conversation, for example, to ensure that people know who is responding to which post. Some do it all the time, others do it some of the time. It's particularly useful on the roll call. Otherwise it would be murder trying to make sense of the different discussions crossing each other!
I use it myself occasionally if I feel there's a need - usually that's on the roll call for the reasons I've just given. Sometimes it's useful if I need to answer any specific points out of a longer post. Far better to use the actual words someone has written rather than trying to get the gist of it across. Less chance of misunderstandings, for one thing.
Sometimes it's useful because occasionally members have changed their posts and the response's meaning has been changed. This doesn't happen often but I know I've changed some of my posts when I've realised that what I wanted to say wasn't quite what I'd actually written and it needed to be changed. Occasionally that would be after someone has responded and the danger then is that their response might have been made meaningless.

I use it myself occasionally if I feel there's a need - usually that's on the roll call for the reasons I've just given. Sometimes it's useful if I need to answer any specific points out of a longer post. Far better to use the actual words someone has written rather than trying to get the gist of it across. Less chance of misunderstandings, for one thing.
Sometimes it's useful because occasionally members have changed their posts and the response's meaning has been changed. This doesn't happen often but I know I've changed some of my posts when I've realised that what I wanted to say wasn't quite what I'd actually written and it needed to be changed. Occasionally that would be after someone has responded and the danger then is that their response might have been made meaningless.