The thing I didn't understand prior to birth, is that to a large part, it's luck of the draw whether you end up with an easy birth or in so much pain you feel you need an epidural. And that the range is huge and to a large part beyond your control.
With all this talk of positions, hypnobirthing, etc etc, it gave me the impression that labour pains were something that could be managed with the right technique / environment / frame of mind / positioning.
But that's not how I see it now I've experienced it.
When you give birth, you will experience some pain. But no one can tell you before hand how much pain. This may be manageable, and within the range that positioning, hypnobirthing, environment, frame of mind etc can make a lot of difference. Or it may be so extremely, unimaginably painful that tearing or needles in the back are the last of your worries.
Asking how painful labour is is like asking how painful an accident will be! For some, minor cuts and bruises, for others pretty bloody painful indeed.
And people saying "I didn't need an epidural" only relates to their own labour. It doesn't mean that labour in general is bearable without an epidural. It means that for some people it is.
The OP asks "what's the reasoning behind choosing an epidural".
For many of us, there is no "reasoning". It becomes clear that the pain of labour is going to be unbearable (and I'm not using that word lightly) and then screaming for pain relief is an instinct, not a reasoned "choice".
I would urge against cutting yourself off from that possibility. I'm not saying choose to have an epidural now. But making sure one is possible is giving yourself a back-up. Friends of mine have been traumatised by the amount of pain they had to endure without really understanding that it might have been a possibility.
I hope I'm not scaring people here, it's very possible that your labour will be totally manageable! But it's rash to cut yourself off from help that you might need in the event IMO.