Sensible stuff, provided you know that the available flight attendant is suitable for the task and situation. Sensible if you have sufficient time to brief them on what you want them to do and not do. Very sensible indeed if they have a flying license of any sort. Absolutely essential if you simply want to cover your back at the inevitable enquiry.
Having said all that, with only a typical cabin crew sample to choose from, I'd rather operate single crew than add to my workload for absolutely no good reason. That could be achieved, to some degree, without exposure to punitive action during the enquiry, by confining involvement to the reading out of checklist items (at least, according to any Company procedures I've ever been required to comply with).