If I understood You right, due to unable invoke XMB by PS Button (which not exist on DS4), You pressing PS3 back button cutting off power? If so, that's very bad idea. Because if game caching data in that moment, one of partition (dev_hdd1) can be simply corrupted which cannot be fixed on PS3 side, by other means than format entire drive (possible on PC, but You need Yours EID Root Key). If You mean pressing/touching and keep pressed/touched power button/touch button, then it is fine (annoying to You but safe to HDD data).
Save data can be corrupted, just like partition on which it is saved (dev_hdd1) if You turn off console during save creating or overwriting. No matter the method You use.