I’ve freelanced for about 13 years and it was always a mix. I tended to keep consistent ones over the course of years and then there would be random ones that would either only use me once or twice because they just needed an IDer for that project (when normally they don’t need one), or it was someone doing similar to what I was that just needed backup help occasionally if they were flooded.
The ones that used me consistently, it was almost like I was salary, but I was kept away from everything so they could always count on me coming in and bringing a unique perspective and not be molded already by their techniques or style. Or if it was technical work, they knew I was good and fast so I was basically part of the special teams or “in case of emergency, break glass” designer that could come in and bang something out, or cover when the fulltimers were away and keep things running smooth.
Ideally, you want to have some steady clients. Five of them that you can keep in steady rotation with and you’ll have decently consistent work. You don’t want to base your entire freelance on the emergency weekend project clients, that would be torture.