I have about even numbers of both, and don't have a major preference.
On long winter rides (being away for a few days) being able to change shorts and wear the same longs saves some luggage space. They can also be pulled on at the roadside at the end of the day when it's getting too cold to wear shorts. As you say, they do also give the ability to wear those older thinning shorts, which are still comfortable (but not so comfortable viewing for the wheel sucker behind him). My best pair of winter tights have windproof/splash proof front and normal roubaix rear, no pad.
Throwing on a pair of tights with no shorts is faster to dress, and less faff doing a loo stop.