There is three things you can do:
1- No use of limits - you just go to any spot and "ref all" and that is your home position
2- Soft limits - you don't have any switches and define to Mach the machines travel extents. There is a write up in Members Docs on how to use / set up soft limits
with no switches , you can turn them on and off ( I found it to be more of a PITA )
3- Hard limits - you have switches which will stop the axis movement and then provide a repeatable home location
All depends on how you work and level of automation you want. If you use no switches or soft limits just be aware that when you turn the machine on the motors will recieve a pulse
and you are not "exactly" at the spot you left the machine. Should you use soft limits and happen to bump or move the axis manualy when the machine is off then the point you defined as home is not the spot you were at when you shut the machine off. If you have switches and they are accurate then you home the machine before use and you are at the true machine coordinate of 0,0,0.
Your choice, do as you wish......
RICH