Most of the software has provision for an endstop at either end.
Depending on your own choices, endstops are not even used. I just position my print-head where I want zero to be on my print, and hit GO.
One thing to note though, is if you arbitrarily decide that your X min stop is on the RH side of your bot... things that you print will come out mirror image from how they are modeled.
Don't ask me how I know this... ;-)
Al...
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