Warhammer 40,000 – When I'm painting my own models often what motivates me to get something done is an upcoming event. It gives you a solid goal to work toward and keeps the focus on only the models you need for the list you're using in the event. A couple of marathon paint sessions and it's easy to get an army at least table top ready in a short period of time.
As a commission painter I often get clients who need to have models painted in time for an event. As a player I completely understand making last minute changes to your list. These can be because of changes to the meta you expect to face or often because the list requirements are some confusing local preference rather than the standard game. Either way you wind up with a unit that you need to get some paint on quick.
Earlier this week my Black Legion client dropped off some autocannon havocs that he needed painted up for an event next week. I do have a full plate at the moment but I always do what I can to accommodate rush needs. Usually for a small rush fee.