Boot sharpers are used when storing the riding boots between riding sessions to keep the shafts of the riding boots straight and slightly shaped. If you want your riding boots to keep their shape and not "sag" down more than necessary, then you should use boot shapers.
An important detail is that you let the boots dry properly before putting on the boot shapers, otherwise there is a risk that the fine leather on the inside of the boots will mold and the boots will be destroyed more quickly.

Cavallo boot shapers sold in pairs.