As I recall, the docs suggest that once you have an optical flow sensor and a proper lidar installed, you can simply use Loiter - and not worry about FlowHold.
From my initial tests now that I have a HereFlow installed with it’s lidar disabled, and a Lightware LW20/C installed - I’m thinking that FlowHold does perhaps a slightly better job holding position. My tests today were at about 2 meters, over grass/turf.
I’m guessing that using FlowHold, that GPS information is either ignored or weighted less in computing position. It would be interesting to know exactly.
BTW - with the Lidar enabled, the copter indeed rises appropriately when hovering over lawn furniture - I’m looking forward to trying a few terrain following missions. And maybe adding a forward facing lidar for object avoidance.
ADDENDUM: I just got back from test flying in an open area where the winds were slightly breezy. FlowHold did not keep the copter very stable in these conditions. Loiter continued doing it’s excellent job.