We recommend auditing your channel quarterly or more often as needed. But more important than finding problems is fixing problems. If you fix every major problem, you won't need to run audits. But if you don't, you'll have to go back occasionally to optimize your videos.
Once you start using TubeBuddy regularly, you can schedule audits for every new video you publish. This way, you can double-check that everything is within YouTube guidelines (such as replying to comments or fixing broken links).