As far as 'best practice' from a theoretical point of view, I have no desire to address the subject at all.

As far as 'best practice' from a practical point of view, I consider it foolish to go for a long ride without the tool to tighten a crank arm bolt, whether that's a socket wrench of some kind, or an 8 mm allen wrench. Of course the crank arm shouldn't come loose! But... it can happen.

One time, on a bike I had ridden only a couple hundred miles since building it up, a crank arm came loose about 20 miles into a 100 mile ride. Searching through my tool kit I found I had not brought an 8 mm allen wrench (which was dumb) but I had brought three different 4 mm allen wrenches (which is arguably even dumber). But to my surprise, three 4 mm wrenches work pretty much as well as one 8 mm wrench. This does not explain why the crank arm came loose, or excuse the mechanic who allowed this to happen but the fact is, this can happen. Be prepared.