[cube scramble="R2URUR'U2R2U2"][/cube] EDIT: Whats the correct syntax to get an cube drawn?
Consider the case when just two F2L slots are left, an edge of on slot and an corner of the other slot is already filled.
Doing a D-layer move , doing XLS (mixed last slot), undoing D move : is an obvious strategy to finish F2L with just one slot operation instead of two.
While being more of a lucky case in Fridrich this can be used actively during blockbuilding in ZZ or Petrus (there it is even simpler to do the recognition because edges are oriented)
When I first tried this (at the beginning of my cubing career) I thougt xls-recognition is impossible to do. But when I revisited this idea a month ago, I was surprised that my recognition time is as fast as normal. But there is only one edge and one corner left so matching colors are not so importend any more.
I still had some problems because for some F2L cases I only knew the first moves, and continued "as obvious" - but with a mixed slot obvious doesn't look obvious any more.
So using xls forced me to get better at F2L execution in general.
I solve the mixed slot at FR or BR position so I only use R and U moves , I think it really helps to have oriented edges when you start trying this, but it si not necessary at all later.
If you already use this (it's not that much genial) please post, because I'm interessted in your experiences.
If you don't use it already - try it - it's for free
If you believe it's too difficult to use, make a comment what's you F2L style is, please.
P.S.: This can also be used as a cheap way to prepare L2L4's CO step.