Actually it's not that great in LC. If Swords Dance/ Bulk Up/ Calm Mind/ Nasty Plot is available, then Work Up is inferior to all of them.
Some Pokemon that can learn Work Up can't learn any other boosting move, e.g. Glameow, Eevee. There are others that are meant to be mixed sweepers, like Virizion (non LC example), or Eevee. There's also Baton Passers like Deerling, who can use Work Up and then pass to either a physical or special sweeper depending on circumstance.
Generally speaking, Work Up is an option for Pokemon in LC that don't have access to other boosting moves (since many lower evolutions lack a lot of moves available to their higher evolutions), or are mixed sweepers. Other than that, Work Up is just a bit more viable in LC than in the higher tiers.
