Quoted from Boatcat:
The coin lockout's purpose is to keep from stealing the customer's money. it should de-energize not only when the power is off but also when the score motor is in motion.
The score motor thing makes sense, clever of them. My uncle and I were playing two player when he stopped over for Easter on my Gottlieb Wild Life which I wired for free play and he just kept pressing and pressing the start button and you can see how it would rob you credits when we had some loaded up from replays and matches, although that one you need to press the start button first so really if you don't follow the instructions (ball in shooter lane, then press it again) you'd get robbed regardless. Tried so hard to not shout out "WAIT FOR IT TO RESET FIRST BEFORE ADDING THE SECOND PLAYER", like I'm some kind of talking instruction card, lol.
Also, a perk to doing what you did is that on the kind of rare chance that somebody did mistakenly put a coin into your games (not knowing they could just play), they'd always get it back. I don't bother to disconnect it on my games but I think most of them already are disconnected, dead, both, or just missing in whole.
It can be common to find an SS machine that hasn't been played much (or at all) since route but usually with these EM machines I have found that they have almost ALWAYS been owned by one or more people already having it in their home (seems like an EM in the basement/trashy mancave was a popular thing in the 90's for the layman with no pinball experience, and then whoever owned it recently if not the same owner would add another home-owner onto that), so usually stuff like that is already done unless they don't know better. I don't think any of my EM machines have any coin mechs left in them, while all most if not all of my solid-state machines came with them working.