It is for our trips, and it works well.
The difference getting into Tripoli as a formation (even with an hour between first and last aircraft) than individually is huge.
We even tried it for the first time into Malta Luqa last week - again, much easier for everyone (not one tail number was used at any stage).
I'm just intrigued by the fact that, in an area (aviation) where there are instructions on absolutely everything, completing formation flight plans appear to be open to personal preferences...
For all the other valid points, we only do it in hard VMC conditions and everyone gets into the gist of things pretty quickly (even 'formation' take-offs). It's not rocket science, and all aircraft are heading for the same destination, by same route, at same time - so good comms are needed anyway (however the flight is filed).
Safe flights, Sam.