When it comes to nightly features use, it is good to note that a stable compiler, a nightly corresponding to the date beta for that stable was branched out and an arbitrary nightly are different. A branched-off nightly might have had beta back ports for fixing stable features that the nightly will not have, and a nightly feature that is subtly broken on stable but isn't used in std will not have received a backport. So using nightly feature on stable might mean every now and then skipping a stable version, and using a nightly compiler means having to do thorough testing after updating on arbitrary days. Any given nightly has high chances of being fine, but every update brings the possibility of bugs.