Personally I'd bounce it to the middle ring instead of going big-big or small-small on a 3x8, and I don't really worry about it on the middle ring. That last is one of the reasons I took the triple off my BSO and configured it as a 1x7

My rule of thumb, take it for what it's worth is drawing the line at the chain making noise. A few seconds before I shift the rear again, no problem but if it's going to be more than that shift the front and set up with a better gear.

It's not the wear on the chain, unless you do it all the time, but the chance of dropping the chain and the noise. And small-small is a tiny bit less efficient and who wants that for very long. Also if the chain is the wrong length or a link is weak there is a chance of a mechanical failure, but that's not an issue if you maintain it and have everything correctly adjusted. So it's really just a small issue, for a short time.