crontab runs at night if mac is on or in sleep mode if i am correct .
i never leave it on/sleep at night
so should i use YASU ? could i ?
is it safe to clear system logs/cache ?
It's useless and counterproductive to regularly clear caches and logs. Doing so will not improve performance, and can actually impede performance. Caches exist to improve performance, so clearing them removes that advantage.
You don't need "cleaner" or "maintenance" apps to keep your Mac running well, and some of these apps can do more harm than good. Most only remove files/folders or unused languages or architectures, which does nothing more than free up some drive space, with the risk of deleting something important in the process.
These apps will not make your Mac run faster or more efficiently, since having stuff stored on a drive does not impact performance, unless you're running out of drive space. In fact, deleting some caches can hurt performance, rather than help it, since more system resources are used and performance suffers while each cache is being rebuilt.
Many of these tasks should only be done selectively to troubleshoot specific problems, not en masse as routine maintenance. OS X does a good job of taking care of itself, without the need for 3rd party software. Among other things, it has its own maintenance scripts that run silently in the background on a daily, weekly and monthly basis, without user intervention.