If it is true that the fees on Bitcoin Cash will always remain significantly lower than BTC, then it, along with other altcoins, would become the optimal choice for performing smaller everyday transactions. In the case of larger transactions, it would still be better to use Bitcoin Core (for the time being) or altcoins because it's relatively more established and reliable. Although I doubt Bitcoin Cash currently has any reliability issues, it's still hard to tell given how new it is and would make more sense to only make transactions on it where less is at stake. At the same time, it helps ease the burden on the BTC network to confirm transactions by reducing demand.