I had a mobile one, was fine at the time and I had no other interventions as a result. However one of my legs completely froze and as a result all of the pushing was borne down through the other, so to speak, this caused some damage to my sacro-iliac region that none of the medics has been able to categorise satisfactorily and 4.5years on I still can't do sports as I used do or much around the house . It hurts constantly.
the labour was long and ardous though and I honestly don't know what else I could have done, DD1 was back to back
second time round I went for a home birth specifically to avoid being near the option of an epidural, as I think there is probably a point in most labours when the pain is so intense you think I don't care what I just need it gone and I worried I would ask for one at that point
my plan worked and I had DD2 at home and did the whole shebang with no painrelief at all (other than a birth pool which was absolutely fabulous)
but, every labour is different and while you can plan not to use pain relief if your labour is very long and tricky you may have to rethink things. DD1 was over 24hours, DD2 was 3.5 hours...
my advice would be to keep an open mind about it in advance...if you do use an epidural just be careful about all the pressure at the pushing stage being equal on both sides of your body and if you do end up with ventouse or forceps that might not be the end of the world either as long as you and baby are well..
(hope this post makes a modicum of sense at least, I am working and don't have time for the sanity scanner)