FWIW The reason it is called (??) is to make it look like a placeholder.
foo ?? bar makes a function to replace the ?? placeholder.
It is somewhat more readable than an infixed `flip`.
Given my druthers l'd have kept the name (?) for this in lens rather than let it devolve to (??), but too many people complained about taking a name they were already using as (?) was the first operator added to lens without a word frequency search against hackage first. The number of collisions it had in practice was rather high.
It was added to lens because a lot of users were asking for variants of a lot of the lens named combinators that swapped the second and third arguments, so they could compose more nicely. By adding one name, (??) we were able to deflect all of those requests.
Given creative use of multiple (??)'s you can use it to shuffle any argument to last position, but that violates the 'place holder' intuition.
It has the more general type of Stefan Ljungstrand"s version of flip from lambdabot, because, well, everything in lens tries to be as general as possible, but the fact that it works for all functors is more or less an accident that only a few users seem to exploit.
The major uses folks seem to put it to is to shuffle the arguments for things like runState, etc. to put the monadic action last.
runState ?? myState $ do
is a lot less noisy than surrounding the whole do in quotes or giving a name to the action
I remain slightly against adding it to a place like Data.Functor because I don't like randomly stealing operator names and for most applications flip is more clear as the named combinator conveys intuition about its purpose.
It fits into the lens ecosystem where I'm willing to assume a great deal of time invested in understanding local idioms, but I feel it is a poor fit for the larger ecosystem for those reasons.