I might use three or four different tunings in a set. I don't have several decent guitars nor a guitar-tech so often have to retune during a set on multiple occasions. Of course I'm going to keep it attached during the set. But I do switch it off.

Before the days of electronic tuners, I'd construct a set to start in standard tuning and get progressively towards an open chord (cos it's easier to do by ear in that order) e.g. standard > drop D > double drop D > DADGAD > open D. Then in the interval retune to standard and perhaps end in open G.