It’s not necessarily a question of being a fan of them individually. Though occasionally you may find one that makes you happy without needing assistance from another flavor.
It’s more a question of learning/knowing what the flavor (that is being taste-tested) excels at, or lacks, and what portion of your “taste expectations” a given flavor may (or may not) fill, and the role it may play in matching or completing a given profile. 
Frequently.
As you’re probably aware, it often takes a few different variants of a flavor to make a “complete profile” for many mixers.
EG: strawberry (as a profile). It often takes two or three different strawberry flavors to make a “well-rounded” strawberry for use in a mix.
One of my preferences is to combine Ina Shisha with FA strawberry. But you have to know what one flavour lacks before you can know how to complement it. Hence the single flavor testing.