The qualified Yes. Somewhere between saying “no” to a new project or taking on something in an open-ended type of way, be clear from the start on what you can commit in concrete terms.
So, what used to be “Sure, I’ll do your web site” is now more often “Sure, I’ll give you 10 hours and 3 calls over the next month to use however you want.” If nothing else, it helps everyone understand that time is a precious commodity, but it also gets me out of being the de facto manager for every aspect of a project I touch.