dougday,
mikecatts and InitialD are correct but there may be a little confusion.
I believe they are saying that if you change your ride height by using the shock collars then you will need to reset the droop.
Having said that, we prefer to do pretty much what you do.
That is, we will set up for, say, a 6mm ride height and rotate or swap tyres to maintain that throughout the day. This saves a lot of fiddling with droop screws, but a decent selection of tyres is needed to do it.
For a shorter final we might use some smaller tyres provided the ride height is within reasonable limits but we might need some gearing changes to accommodate them.