docs: Note when endstop phases are useful in Endstop_Phase.md

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 11 insertions, 0 deletions

diff --git a/docs/Endstop_Phase.md b/docs/Endstop_Phase.md
index 9b7b4d74..0c09eea2 100644
--- a/docs/Endstop_Phase.md
+++ b/docs/Endstop_Phase.md
@@ -73,6 +73,17 @@ SAVE_CONFIG
 Additional notes
 ----------------
 
+* This feature is most useful on delta printers and on the Z endstop
+  of cartesian/corexy printers. It is possible to use this feature on
+  the XY endstops of cartesian printers, but that isn't particularly
+  useful as minor differences in XY position rarely impact print
+  quality. It is not valid to use this feature on the XY endstops of
+  corexy printers (as the XY position is not determined by a single
+  stepper on corexy kinematics). It is not valid to use this feature
+  on a printer using a "probe:z_virtual_endstop" Z endstop (as the
+  stepper phase is only stable if the endstop is at a static location
+  on a rail).
+
 * After calibrating the endstop phase, if the endstop is later moved
   or adjusted then it will be necessary to recalibrate the endstop.
   Remove the calibration data from the config file and rerun the steps