Ok, Rooting basically gives admin type rights to your phone. I have 2 rooted optimus v's from Virgin Mobile. One is mine. Other is dad's. I have my stepmom's to root still.
Rooting opens up more than just deleting apps. You can partition your sd card, one part FAT, one part FAT32 using minitool partition wizard (Free). After this you can use programs like Link2SD.
Link2SD is one of the greatest values of root. I now have all my apps moved to the sd. It's different from Apps2SD. Basically not only moving certain apps but the whole app or most of it.
To explain better my phone only has around 170mb usable after root, and deleting bloatware without adding any apps. Now with my apps on it, sd partitioned and linking the apps I have placed on the phone it is down to 160mb of internal. Whats more amazing... The sd card is only using 10mb as well out of 8GB.
So this is not the limit to the rooting. Roms are like different OS for your phone. But as of the moment A temporary root is the only kind of root you want to do right now. ICS - Ice Cream Sandwich 4.0 is the newest Android OS. Luckily a work in progress on the official phones to be upgraded. So wait to root or be able to unroot or the update can not be accessed. As they have said it will come out early 2012 so it could even be at the end of the first quarter. So Ice Cream Sandwich is what I am waiting for because my girlfriend just got a HTC Rezound.
Unlocking, allows use on different networks,carriers.
So there is more that you can do. Just look around on different parts of forums. The apps for Rooted phones are not just for certain phones, plus look around the market type in root. Many apps require rooted phones and there are many different things you can do.
Also Virgin Mobile Optimus V, sucked on battery. It has a time without signal bug. Flashing a rom fixes this. However. My fathers phone I have rooted, linked all apps. Added Juice Defender app. Now it has been 1 day, 14hours, 55minutes since fully charged and its at 70%. Meaning the phone will now run for about 5 days or so before having to charge it again.