It's not clear to me what you are saying about the resistance of the wire. To be clear, the resistance for a given length of wire increases as the diameter decreases.
That is, the higher the gauge number the higher the resistance per meter. For the short runs of signal carrying wire in a hand wired amp it is not too big a deal to go a gauge or two smaller. For long runs and high currents it is a big deal.
This has little to do with ease of use. As PB points out small diameter wires get tricky to strip, particularly when insulated with Teflon. They are also more prone to getting nicked from poor stripping technique, which often leads to a break in the wire just inside the insulation.