2 big files in AppData\Roaming\tixati:
* channels2.dat
* channels2.dat.lastloadok.dat

Can someone explain what specifically is writen here, and is it ok if I delete it? From file explorer, or maybe inside tixati itself?

If it's just a channel name/content cache or something, I don't need it all the time when they start to be giant files? Can just reset & start from 0 again?

those .dat files hold ALL your channels information. to see what happens close tixati, copy out or rename both files and then restart tixati. your channels will be empty. if the .dat files are getting too big you have to delete channels that have too many shares for you to handle.