Multiple tickets when flying
Pros vs Cons
Bags are not checked all the way to final destination
If you are on seperate tickets and changing terminals and need to pick up bags and re-check. Suggest at least 4 hours minimum between flights.
Why? your flight could be delayed coming in. Airlines don't cover other airlines.
Long distance between terminals when catch different airlines eg. terminal 2 to terminal 5 at London is 10km apart
Visa entry - if you have to pick up bags, you have to exit, you must have correct paperwork eg. Singapore visa, even though your not leaving airport
Can be cost effective or direct/less transits
Can't book the flights you need on the 1 ticket.