too many buffers

[andrea]

When I use emacs for long times I end up having a lot of buffers.
It's not a big problem but it can be annoying, and there are some
buffers that should just not stay there:
- magit buffers
- dired buffers (I didn't find a variable useful to limit the opening of
  new buffers)
- completions/help/annotate.

I normally use those things once and if I need them again I'll execute
again the function.

Can I limit the creation of new buffers or maybe I should write some
functions that cleans the situation automatically (using ibuffer maybe)?

And also with org-mode when I use the agenda it visits ALL the buffers
without closing them after, is that normal?

I have more than 50 files in the agenda only...
Thanks