it reduces the price the developer has to pay for the flash memory built into the cartridge... if you notice, pretty much every nintendo branded game saved on the cartridge because nintendo has money to spare.
It's always about the money... and the customers get !@#$% over for it. I can probaly get a controller pack under 10 dollars nowadays. But it probaly was way more expensive in the n64 days...
Actually, I picked one up a few years ago for about $1 or so (Brand New). Not sure about where you live though.
Ironic enough, I actually lent it to a guy in my school last year who was talking about needing one cause he was playing Turok 2 I think it was and needed one to save. Haven't gotten it back yet lol and I think he graduated, OH WELL.
Thus, the controller pak* is definitely worth it.
* According to the one I still have, this is how it's spelled.
Yeah that's how it's spelt.