Hi there! Well, the meaning is actually the same. The final particle "si" indicates to whom is directed the action, and it's a way to intensify the message. "si" is quite particular, because suggests impersonality. "E' bene ricordarsi di spegnere la luce" means that people in general should remember to turn off the light. If the particle was "mi", the action would have been directed to mylself. "Devo ricordarmi di spegnere la luce" means that I have to remember to turn off the light. "Ricordami di spegnere la luce" means that I'm asking you to remind me to turn the light off. It's a bit messy, if you have other doubts ask me!