Suite DBs do grow without limit, and they store other information besides checkpoints too.
You can configure Cylc 8 to symlink workflow run directories to other locations. (At Cylc 7 that is up to you to do, or if you use Rose with Cylc you can configure rose suite-run to do it.)
BTW; the checkpointing is very useful.
I wouldn’t come to rely on it as checkpointing has been removed from Cylc 8 for reasons explained in this post: Proposed removal of scheduler checkpointing capability
(Cylc 8 has a better way of restarting at earlier points in the graph)