As Ritesh mentioned, it's usually just a business preference to use KMAT vs configurable FERTs.
However, keep in mind that by default KMAT's do not have accounting views for their material master records. Therefore, one may come across issues elsewhere if an accounting view for some reason is needed for the material. An example I've come across is KMAT's in conjunction with material ledger use. Without a material master accounting view the material cannot be valuated in the material ledger tables so errors can arise when posting goods receipts. Luckily SAP allows the opening of accounting views to be available if need be, but it's something to keep in mind nonetheless.