A founder asked us for one backend developer, part-time, for a couple of months. Two weeks in, most of the work turned out not to be backend at all: a payment flow needed reconciling, the release process lived in one person's head, and nobody had checked what happens when a card payment retries.
The developer they asked for could have handled any one of those. Doing all three in sequence, alone, would have eaten the whole engagement. So we put the hours where the month actually needed them: backend for a stretch, then a QA pass, then someone to make deploys boring. Same budget, different shape.
Now we open these conversations by asking which roles a month needs rather than how many people, because part-time headcount is easy to price and usually the wrong question. If you had one developer for a month, what you would hand them first is the thing worth naming out loud.