When is a fuse used in tandem with a breaker/MCB?
It actually does not make a difference if you use an MCB or an fuse as long as you choose the right size and type.
It is usually a question of money and convenience as MCBs are usually more expensive but provide the convenience of not needing a replacement if tripped.
If a fuse and MCB are used in the same circuit then the fuse usually will protect more than one circuit and is a lot bigger than the MCB so it doesn't usually trip and because it rarely trips you don't really need the more expensive MCB.