Some N64 can hold saves on cart and used the pak as a way of transferring saves to another cart. other cart do not have any onboard memory save and requires the pak to save game. Is there a list of games that requires the memory pak to save game? I can only think of Quest 64. Mario Kart 64 only needs it to save ghost data and it's not required at all to play.
Some games used different save methods for other regions. Castlevania saved to the cart in Japan. Instead of controller pak.