The biggest part of rooting the Thrive would be for customization. Many people like to have custom bootloaders, and other ROM's that get rid of the 3GB limit on apps. Others like to overclock, others yet like to underclock... it's all about choice. I know that I'm rooted(I did this a short while ago),a dn have done 2 nandroid backups just to make sure my tablet was always safe.
But like I said, it's all about personal preference. Please note, though, that if you do root, you lose access to google play movies. There are soem other things too, but I'm not sure what they are. Mostly rooting, in my eyes anyeays, is a positive thing, and I would say, if you want to root, go for it. You can always unroot.