I rather like 4-3-3 against teams that play three at the back, like Napoli.
The winger are able to exploit the space behind the wingbacks are move CBs into positions they don't want to be it.
Fiorentina played 4-3-3 in the 0-0 draw they had with Napoli and should have won the game.
Cerci caused them so many problems playing in the space between Napoli's left CB and Dossena that Napoli changed to playing 4-4-2 to try to close that space.
That change to playing 4-4-2 upset Napoi's rhythm and caused them to be much less of an attacking threat than normal.