I used to panic about these things, probably because they were arranged weeks beforehand, the date and time would be up for everyone to see and it felt like you were being 'observed' in the run-up!!! (paranoid!).
However, once in there, I found an appraisal to be beneficial, although the courses I was promised never (ever) materialised (or someone else went!)
. I think that as long as whatever is talked about/arranged is followed up they are a positive idea.