The poly bushings can cause suspension binding...thats not good. Im not going to explain because it can be found by searching. I am honestly surprised they still make those things.
If youre going to replace them, go with mugen or oem (I believe oem is now available - they werent before). Replacing is very simple and straight forward...you can do it yourself.
I replaced mine with mugens when I did the rear disc change-over.