Applying the throttling hack removes the initial data limits placed on your phone. Your internet should be faster once the hack is applied (if it is applied correctly). Disadvantage is the same with any hack you apply, as it has the potential of getting you into trouble with vzw. Also, in the rarest of cases, you could do damage to your phone, but I have yet to hear of this happening.
I've heard people say the throttling hack is pure placebo effect - I've never used it so I can't say for certain, but you should know there are two very distinct sides regarding the throttling hack.
It's possible that throttling may only be done in certain high traffic areas or peak times.
The replacement of the services.jar file can mess with a theme & some themes replace that file when flashed.
Awesome. Thanks for all your input. I found a services.jar made from my current theme and I have to figure out how to change permissions for some files cuz I cant get em to change but thanks everyone