How does my printer auto level based off the sensor I installed?

Question

I'll start off with some info in case it's needed, but my questions are a bit lower. I have an Ender 3 Pro with the 4.2.2 motherboard. Grabbed a Marlin firmware bin from Shiny Upgrades and seems to work great (built my own once and wasn't a fan). Got my Z-offset sorted out with a combination of stealing other people's numbers and testing a few prints out. Tried auto homing, but got weird numbers and instead resorted to that other approach. Printer seems work well now and my Z-offset is around -0.8 mm.

• Is the Z-offset I set in printer UI the distance between the sensor and the nozzle?
  If so, does that mean I can now swap beds and expect the printer to automatically adjust for that without having to adjust the Z-offset again? Maybe assume I'm swapping between two perfectly flat beds and one is 5 mm thick and one is 10 mm thick, so we don't have to account for a different bed level mesh or something.
• Is my bed leveling kind of useless?
  I have 7x7 leveling, but the sensor is quite the distance away from the actual nozzle (mainly on the X-axis, but I assume also on the Y-axis), so any point it levels for won't actually be the point where the nozzle prints. I don't recall seeing any X or Y offsets in the printer UI either, just the Z offset. Why would the Z offset be an adjustable value in the UI, but not the other two? Barely anyone even mentions setting an X-offset and I'm not sure why.

Answer 1

Is the Z-offset I set in printer UI the distance between the sensor and the nozzle?

From this answer on question "Z Offset on autoleveling sensor setup" we read that:

the offset between the nozzle and the sensor trigger point (to the bed)

If you replace the build surface for a different surface the offset doesn't have to be changed.

Is my bed leveling kind of useless?

No, automatic bed leveling can be very useful if the build surface isn't as flat as a sheet of glass, it will map the surface and ensures the first layer is deposited at the correct distance.

I don't recall seeing any X or Y offsets in the printer UI

These settings are in the firmware, that is where these are defined. Note that these shouldn't be in the UI, as this is a hardware change. Also note that Marlin is pretty well programmed and is aware of this sensor offset, and even will use these offsets to have the print head (nozzle to be exact) stay within the specified print area. This is a good thing, e.g. when the sensor offset is large, and it would probe to the edge of the bed, the head could potentially wreck one side of the printer. This is described in question "How to set Z-probe boundary limits in firmware when using automatic bed leveling?".