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Flowing nitrogen is just plain good to do.

I suppose you can go over the top if you work at it a while, but the A2L protocols require it everywhere now, so giving my guys a choice to do it or not will just confuse them. ALL VRF systems require it for the extended warranty & likely the regular warranty. Flowing nitrogen will flush contaminates & moisture out of the lineset, your vac will pull down faster. You have to have the bottle out anyway for the pressure test.

No down side. Except, I guess, toting the bottles up the ladder to the roof. That's hard.

pretty sure the manufacturers of r22 equipment required it too

You can also use Co2. We used that with the small aluminum tanks. It holds a lot more gas than a nitrogen tank and a lot less weight.

I use 40 cu ft bottles when I can, 80's when I can't, occasionally 125's, and once a (well, many, sequentially) manifold of 12x 200's.

Not sure about flowing CO₂ during brazing. I'd think that the temperatures may lend themselves to breaking down the CO₂ and then we're back where we started; but I admit to never having actually checked that such is the case. The bottle threads are different, IIRC.