If I could reduce my army's size in points and get command points for it, what ratio would make it worth it?
Obviously, if it was 1-to-1 (I could give up 10 points to get 10 command points), I'd totally do it a bunch.
If it was 10-to-1 (I could give up give up 10 points to get 1 command point), I could well end up exchanging a few points, like taking a 1980 point list with +2 command points against my opponent's 2,000 point list. Certain Craftworlds stratagems are worth it, particularly Webway Strike.
If it was 25-to-1, I might consider exchanging 20 or 30 points for a single command point, in a list that _really_ needed it. But at this point, you are saying something like "would you like an extra Fire Dragon?" which... I mean, I'd often prefer the extra Fire Dragon.
In my lists, which have a medium amount of command points, I'm often willing to usually spend a command point to get a victory point, like using Matchless Agility to tag an objective to complete a Maelstrom card.
PL and Points don't convert evenly with each other, so I can't say regarding those.