This setting allows you to decide what to use as the "height" when determining the building classification in 4.1.7.2. This classification determines whether he Static procedure from 4.1.7.3 used by Shearwalls is applicable to your structure.
The choices for the height to use for this purpose is
A choice has been added in this regard because the all-heights procedure is intended for flat-roofed structures, but because no other method is available for multi-block structures or narrow low structures, it is used by Shearwalls in cases that there is a peaked roof. This setting allows you to apply your discretion as to what height should be used for your structure.
For low-rise structures, it is clear that each height H is used in 4.1.7.6.(1) for the restrictions on these structures.
Note that this choice affects only the operation of the program in general and is not saved with the particular project file it has been applied to.