Like several similar tasks, the actual act named in the verb takes only a portion of the time. For painting, there's layout, there's mixing, there's setting up ladders and shifting things around to get access (and laying out drop cloths over the things you don't want paint on), and there's clean-up.
I finished off the week with six hours on my feet with my hands in cold water, cleaning brushes and buckets. I'm still sore this morning.
A significant part of technique -- a big part of what I've been learning on the metal lathe over the past few months -- is achieving two somewhat paradoxical goals in regards to the verb; to increase the relative proportion of time spent in which tool edge is actually touching work piece, and to increase the rate at which material is removed (or in the case of painting, added).
I've been introduced to a new paint technique and I like it a lot. I've done speed-roller painting for floors before, and used rag rollers and die-cut texture rollers, but I've never done an entire set using dry-roller and roller feathering as the primary shading and texture method.
There are downsides. It takes concentration, slip-ups are inevitable, and their correction is difficult. It takes only a fraction of an inch of too much wrist rotation, or an ounce too much pressure, to put a hard roller-edge line in the middle of a softly feathered gradient. And it can't be corrected without going back and extending the entire gradient. Rollers also take a lot longer to clean, and can't be put back into service immediately.
Unlike, say, brushes, which can be put back into service damp, and can in a pinch be wiped off on a scrap or a rag and used on the spot. Which means roller feathering shines when there is a small number of colors, but gets labor intensive when there is a large number of colors happening at the same time. Among other things, the sheer effort in juggling multiple roller pans begins to add up.
The upside is of course speed. Rollers hold a lot more paint than brushes, meaning fewer trips to the paint pot or roller tray, and when you are using an extension pole this can be a significant saving in arm motions. In the right places of the work, you have the full width of the roller available, so it is like feathering with an 8" wide brush.
For smaller sets and detail work I'm not going to give up my 2" sash brush. This is a tool I found after several years of experimentation. It is a generalists' tool; it doesn't carry as much paint as a 4" layout and it isn't as easy to get in tight as a detail brush, and it is too clean to make a good dry brush (the best dry brushes are old, fuzzed-out brushes of just the right level of hairy disorder. Like a clarinet reed, they take a while to be broken in to this perfect state, and you struggle to keep them there as long as possible). But the 2" sash will basically do everything.
This was my previous time-saver; the 2" sash and a rag, meaning I could keep moving without having to change brushes, wash brushes, etc. All I had to do was change the amount of paint captured on it and the way I applied it to the work, shifting without any perceptible pause from laying in a patch of fresh color to feathering out a detail to cutting in hand lettering.
Theater techniques are, unsurprisingly, about speed. They are also about coverage; a typical regional theater seating 400-2000 will have a proscenium width of forty to sixty feet and a height upwards of twenty-five. A full-width drop, then, is easily 1,800 square feet. If it is new material it could take four gallons of paint to just cover it once. Fortunately most theater drops are recycled, but it will still take a couple of gallons to get some color on it.
Also fortunately, theater is about scale; in many cases we are trying to simulate real materials, in most cases we are adding extra texture and shadowing and detail just in the same way and for the same reason the actor accentuates their natural features with make-up (so the people seated sixty feet away can see something), and in many cases we aren't trying for realism anyhow.
So there are innumerable texturing and detail techniques to bring in wood grain, grime, marble, wall paper. And these are almost all techniques that are done with large, sweeping motions with the biggest tool we can use. Probably the subtlest and slowest technique that has common application is spattering, the poor man's airbrush. This is done quite literally by hand (or on a aptly-named Spatter Stick); you carefully get just enough paint on a brush, then you slap it repeatedly to send out a haze of fine droplets of paint.
Needless to say, with two weeks and a crew of three to cover four full-stage drops and three wagons on a 100' foot apron with 20' high walls, we are not doing any spattering.