The combination of Imposter and Choice Scarf allows Ditto to function as a formidable revenge killer, punishing opposing setup sweepers by copying them and their boosts while also outspeeding them thanks to Choice Scarf.
Due to Ditto refreshing PP each time it switches out and its ability to copy opposing support moves, Ditto can also give its team an edge in PP wars against defensive threats.
Ditto finds a niche on defensive teams that appreciate its ability to revenge kill threats that the team otherwise can't wall as well as Ditto's potential to offer some form of offensive presence and stalemate opposing defensive teams.
However, Ditto is unable to revenge kill some common threats, notably setup sweepers carrying Substitute and Calm Mind Arceus formes. Additionally, Ditto does not copy the foe's HP stat, and thanks to the high HP stat of many threats in Ubers in comparison to Ditto, as well as Ditto's lack of a boosting item, it cannot win one-on-one versus many common threats and requires them weakened in order to effectively revenge kill them.
Furthermore, due to its low HP, Ditto requires free turns to safely switch in, either after a teammate has fainted or through pivots, and may force risky plays in order to to bring it in without having to sacrifice a teammate. Ditto also has little defensive synergy in terms of walling threats, leaving its teammates often overwhelmed by offensive threats before it can safely come in to attempt to revenge kill. This compounds its unreliability, as immunities and resistances to the moves of the sweepers that it copies are common, and due to Ditto's Choice Scarf, it must correctly predict if the opponent is switching out, as well as the incoming switch-in, in order to claim a KO.