The ability to have multiple fields in custom forms that are linked together in a relationship such as:
Choosing a value from Field 1 determines what is available to choose from Field 2.
Choosing a value from Category determines what can be chosen from Brand which can then determine what can be chosen from Sub-Brand.
This would be better than:
In the example above: a huge long list of choices in Brand and Sub-Brand in order to encompass all Categories and Brands.
In the example above: The workaround of having multiple "Brand" and "Sub-Brand" fields with hide/show conditionals plus awkward "ifblank" reporting concatenations.
Whether this was via the Builder or some more back-end method (like a Kickstart) is fine by me. I honestly think a matrix Excel uploaded via the backend might be "easier" and then just a Builder UI element that is dropped in and linked to the Excel data. But...I leave such issues to the developers. :-)