I recently bought a new mac (Ok the University bought me one.) Anyway, since it has a larger disk, I now have about 30 Gig free on it. It is so hard NOT to empty the trash. I am tidying up various things and the other day I emptied the trash and then realised that I might have deleted something I need. Since I have multiple gigs free and much less than that in the trash, there was no need.
Just now I have, amongst other stuff, a 15 Gig file from a virtual machine in the trash. Since I still have 30 Gigs free after that there's no mileage in emptying the trash just now.