Hard reset dumps all of your temporary memory on the device. This leads to less problems such as call logs, MMS, and emails "disappearing."
Whats a soft reset? (lol j/k I just don't ever do a soft reset)
I pull the battery at least once a week as a minimum as preventative maintenence.
If you are using sometype of hard case or skin, I recommend the Program:
Soft Reset (even though it implies a power down, it does the exact same thing as if you were to remove your battery)
Download via OTA
or Using Desktop Manager.