Actually 1+F may be the perfect choice in a holding when heavy or for longer flights with a certain speed. In Conf 1 the speed may be to high and you may not want to have the extra drag given by Conf 2 for ... let's say 25 miles.
Anyway it's non standard and should be announced before and agreed by both of you.
Also CONF 3 in gusty conditions works great, it feels a different airplane and the gust won't push you the same like in FULL, however keep in mind the difference in flare (lower, a little firmer but thinking about the tailstrike limit) and the float (actually lack of it).
And finally for the first post in the topic, there is NO limitation on using both in the same time but thinking about the load i think it's just basic airmanship to do it one at a time (unless you're too close to the runway and looking to stabilise ASAP).