I'm not an expert - but your SteemPower for the day is divided by the number of likes. So if you have a $1000 worth of value to give, and only make one like, that post gets the entire $1000. If you make 5 likes, then each post gets $200. It keeps going down the more you like. Undoing likes resets what your previous likes have got. And if you "rest" for 24 hours, the power restores itself.