The inputs on my MX4660 for my DIY control system currently uses a dedicated input for Y1--, but I have tied my Y2-- and Y2++ limit switches into a single input. I'm not having any problems with this configuration. The machine homes and the limit switches stop the machine like they should. I have a couple spare inputs that I'm not using. Is there any tangible benefit to putting Y2++ on its own input? I can't think of any, but I figure what the hay?