We used to run -stable, and update every few years, like from FreeBSD 9.x to FreeBSD 10.x. We found that when we did that, we would often encounter some small subtle bug that was tickled in our environment, and which was incredibly hard to track down. That sort of bug was hard to track down because the diff between branches was enormous, and because there were thousands of commits to sift through, and because the person responsible for the bug may have committed it months or years ago, and has forgotten about it.
We eventually decided to track the main branch, updating frequently. This means that while we find more bugs, but they are far easier to fix because they were introduced more recently, and there are a lot fewer commits to look through to find where they came from.