[BrianG]

Well, a good solder joint is really important everywhere, but a poor joint in heavy current wires can create resistance which will heat up. A poor solder joint in things like a BEC connection could cause intermittent power to a receiver, which could cause glitching or momentary loss of power (and control). It's really easy to have poor solder joints to cause some very weird symptoms that are sometimes hard to trace.

There is a sticky somewhere here about soldering and the care of soldering tools.