Tiny spot color logos as sleeve prints.. base + 4/5 color plastisol at around 30mm wide.. worth the hassle?
Moosman has a good alternative. The only thing I'd include in your consideration is the quantity. Large quantities would lean more towards screen print. Low quantity, like 12-200, you can heat press. Over that, I'd screen print it.
So if Screen printing, "what is too small" for a multi color print?
I've done sim process neck tags or "Nape prints" as small as 2"wide before. Multi color spot colors at 1"
For those, or even Left Chest sim process, I go with a higher LPI like 65. There isn't much room in the art at those sizes for any good color transition. Very compressed, but it's all you can do. They work out just fine.