In some advanced cases of creating Slices, it would be very handy, and more performant, to base one Slice on another Slice, instead of all of them on the base Table. This way one can avoid having to repeat certain conditional expressions.
Consider this hypothetical example:
The data:
Slice #1 “USA Clients”
Row Filter Condition = [country] = "USA"
Slice #2 “USA Consulting Clients”
Row Filter Condition = [service_required] = "Consulting"
It would be handy to have Slice #2 be based off of Slice #1, which already filters down to USA. Otherwise I have to add Slice #1’s Row Filter Condition into Slice #2’s Row Filter Condition, along with an AND(). Not a huge deal in this simple example, but imagine if that first condition was an expensive SELECT(), and it would be getting needlessly repeated.