I had an epi for Charlie's birth but not my first three kids and the pros are obvious in that there was no pain for the most part.

The cons (for me) was that my blood pressure kept dipping to the point of me starting to lose conciousness a few times. My pressure throughout my pg was around 110/60 so the epi really pushed it down to around 92/50. Scarey stuff - not for me but for my DH and the widwife! The other con was that despite having a light epi (no catheter, I could walk etc) I didn't feel like pushing when I was finally completely dilated. In fact we had to wait about 15 mins for my top up to wear off before I felt like pushing, and the pain was intense after having had nearly no pain up til then.