In the past, I always finished one before starting another. Then.....I had to move my paint booth out of the house. That's fine in warm weather, but when it's cold....welllllll.
Therefore, I have a few (7) builds that are up to the painting stage that are waiting on warm weather to break. I can stay busy at the bench in the winter, and try to play catch up in the summer.
I do have one build that has been going on for more than seven years, but most of my stuff will be finished this year.