post it 
Spectravideo 728 has a microswitch inside the cartridge slot. I have always wondered what it does and only now my two brain cells determined that it must be a cartridge removal safety of some kind.
I think they use the hole when manufacturing.
They pierce a lot of carts in a long metal stick and then they paint them like car pieces... (just kidding !!!). 
I know the hole is only for protection while inserting or removing. Toshiba computers have some kind of switch for this inside the cartdrige slot, also.
By the way, as Microsoft and ASCII defined all the MSX hardware rules, there should be some document describing the cart and the slot specifications... maybe in the Red Book?
See sanyo PHC-28P pcb... uses photocell to reset computer when insert/retire cartridges.
