“poco f” is occasionally seen and it’s not uncommon in the repertoire — this example is from Martinů (“Sinfonietta La Jolla”):
I’ve found it to be most useful with instruments that are inherently “strong/loud” (trumpets, cymbals, lots of high energy overtones) — poco f communicates “play strongly, but be mindful of the surroundings/context; don’t overdo it”. Like the cymbal accent here: even if it’s a “solo”, it shouldn’t be too loud. But marking it “mf” would likely leave it too subdued.
But it’s definitely a “Catch-22” dynamic. If you’re wondering if you should use it or not, then the answer is no.