Sure, the owners would not be happy. But slot machines are installed all over the world and not just in casinos.

The idea was not to take the machine apart but to try to glitch it by hitting metal parts that were not properly grounded. This would then allow the voltage spike to make it into the circuitry, either leading to breakage, no effect, or fault injection. The latter could sometimes be converted into a win on a subsequent spin.

This is 80's stuff, I'm pretty sure todays' slot machines are tamper proof to the point that trying this is totally pointless, and even back then hardening against this was common.