No, I don't keep it forever. Even at 3fps plus audio, it adds up. I tried 1fps before, and it was not enough, interfaces move faster than that. 3fps is sufficient, but sometimes I boost it for more important things like when I am teaching.
I usually review them and take a few snapshots before deleting. Some I keep longer.
AMD and Nvidia Drivers can both be set up to record the X last minutes of the screen. I've found it very useful when logging bugs to be able to step back through my last few minutes to see the steps that led to the bug.
We're building a startup based on this idea, though we find that the #1 use cases is catching unexpected bugs. Is that what you find as well, when recording with OBS? Check out http://replayable.io.