In a nutshell cluster feeding is basically a baby's method of communicating its mother's body to produce more milk.
Nursing is so much more than nutrition and is also a method of communication for a baby (particularly a newborn) and suckling can be one of their main forms of self-soothing and comforting - in short it makes them feel good and ensures they stay close to Mum! Some babies will also cluster feed as a way of "tanking up" before a long stretch of night sleep.
Cluster feeding will quite often coincide with a baby's fussy periods so a bottle fed baby can still be fussy or cranky at a time when they might cluster feed if they were breastfed.
Ultimately I think that if you were to bottle feed (either breast milk or formula) rather than cluster feed your body would miss the cues to produce more milk so your supply might not keep up.