My previous employer used to plan "express checkout" weeks for developers. In between two larger projects, you'd get the chance to spend two weeks doing nothing other than picking low-hanging fruits off the bug-tracker tree. It worked miracles, with minor-but-irritating bugs getting solved much faster, and with features for niche groups getting implemented as opposed to laying in wait for a bigger project it would th…
I worked at a place once where my favorite time was at the end of the year; most people were off on vacation but they needed a skeleton crew in case of issues. This was when we did tons of small bugfixes, improvements and refactorings, and honestly that's the best part of the job IMO. Screw building features and adding customer value, just let me do janitorial jobs :D