CS 3 - CS4

Is there a reason to keep CS 3 on the computer when I also have CS 4 ?
Will CS 3 do anything that CS 4 does not or can not ?

I have one obscure (but important) plug-in that will run on my old CS2, but not on my CS4, so for that reason I've kept CS2 installed.

If it wasn't for that, I wouldn't have kept the old version. I can't think of many reasons to do so.

Unless you have a situation like Damo had, then no.

The few plug-ins I have seem to work . Thanks . It has a major layout change and did not know if something was left out rather than upgrade .
I have not even opened Illustrator yet .