I basically work exclusively on projects since my goal is to develop a body of work whose total is greater than the sum of its parts in order to tell a story or communicate information.
My projects are infrequently as short as six months but others have been ongoing for five to eight years. I currently am working on two projects, about five years into each. As both are geographically distant, I will sometimes go for a month without photographing much. But I do have another local project, about eight years ongoing now, that I will pursue when I find something that I think will fit.
I have had a large number of projects that got abandoned after six to twelve months when I deemed that they were not coming together into something meaningful.
Of course, I will not pass up the odd unrelated shot when I happen to come across one by chance. But I spend about 15 years wandering around directionless and simply looking for something interesting to photograph. I have very little to show for that time and effort.
A bonus of only working on projects is that it will eventually force you to be a critical editor and tolerant of time and effort spent with ultimately nothing to show for it. It is hard to force yourself to end up editing out 100% of what you spent a week shooting after driving for 12 hours to get there or an international plane flight, but it is necessary.