... besides that what and how does it exactly work?
Ok so how does it work?
The BaaS provider runs and maintains the nodes.
As a consensus mechanism, Microsoft Azure for example uses Proof-of-Authority.
Why would any company need a slow and inefficient datastructure if they don't need the one advantage of it - decentralization ?
Well maybe areas that require many transacting parties, like the supply chain.
Or to store critical data in an fault-tolerant way.
Consider a private blockchain as a p2p database, which guarantees robustness and fault tolerance.
A blockchain does however not necessarily add value.
http://doyouneedablockchain.com/