Proof, as if needed, that the word 'Formation' in a post can chill the blood of some and raise the blood temperature of others.
Suffice it to say the term formation if correctly used has a clear meaning to do with primary references and responsibility of parties. A loose gaggle is a different matter. There are many posts on this.
It is simple if you haveny practiced and briefed then there is a clear answer - dont do it.
Personally I would rather be five feet from an aircraft knowing where it is than fifty feet or five hundred feet and wondering where it has gone. BUT I have trained and practiced.
Having said that I was once in a jodel with no instrumentation on a club fly out over the channel and took the opportunity of tagging along with a Cessna 150 for the return journey. He had instrumentation. The vis meant that I could only just see where the water and sky were. Much easier to keep the right way up following loosely his wing as a horizon.
It was the safer option but I still wouldnt advise planning to do that.