Over on The Pragmatic Programmers, I wrote an article about spreading the work fairly when you have infrequent contributors. This is a common issue in open source projects that have people who work on them as their full-time job.
Contributors are the lifeblood of an open source community. You want to attract and retain people so that the project is healthy and sustainable. By carving out space for your infrequent contributors, you keep them engaged. Maybe they even grow into more frequent contributors.
There’s a benefit for your frequent contributors, too: managing stress and burnout. Even when you enjoy the work, when you become a single point of failure, that adds a lot of stress and expectation. Over time, what you once enjoyed becomes a burden. By developing a culture of waiting, your frequent contributors learn to pace themselves. This measured flow makes your project healthy and sustainable for frequent contributors, too.