As a formation it saves a lot of hassle and delay getting down (as described above)
For fast jets it's the only tactical way to land i.e. shortest possible time flying slow in a circuit, hence the need for fast jets to practice it (although when they do it at civvy fields it's possibly just coz it looks punchy
).
Thers is no
need for civvy aircraft to do it (unless they're in formation) but it's bloody good fun and it is another type of approach, can't do any harm to have another trick up your sleeve can it?