As far as whether you need to delete them.... you don't have to, but regardless of the OS, most of us like to every now and then.
I do mine every 2-3 months, not that I really see any difference
Overall, you don't get the bloat in OS X like you do with the Windows registry, so ultimately, maintenance is minimal.
The application of choice for many of us here is definitely OnyX.
It is a free utility that will take care of things.
If you're unsure as to what everything does, just use the automation tab with the following checked (which I think is the default).
Be sure to download the version relevant to the OS you are running(scroll down the link to get the older versions).
Download OnyX for Mac - OS X maintenance & optimization tool. MacUpdate.com