lightning network – Why are multi hop virtual payment channels desirable?

There are papers about multi hop virtual payment channels emerging linke the Perun paper or more recently the Donner Paper.

The idea seems to be to reserve some liquidity on a path (or potentially flow) of channels between two peers for a longer time to effectively give them a virtual channel in which they can transact as if they had a direct channel.

Why is that better then just using the available liquidity everytime one wishes to transact?