Why subnetting of IP address is done? What is the difference between subnetting and supernetting?

In general, subnetting breaks the bigger IP subsets  into smaller while, in super netting making large IP sub nets with the combination of Small IP sub nets.

In actual, sub netting is transfer of host bits into network bits however, in Super netting transfer of network bits into Host bits.

Subneting is breaking of bigger subnet into smaller subnets.

Supernetting is making big subnet from smaller subnets .

Supernet is also called as route aggregation ,normally used by ISP to advertise bigger supernet rather than smaller subnets,