Like all agencies, UX agencies are specialist companies that do a task for their clients, rather than them having to do it in-house. In this case, the service UX agencies offer is designing the user experience for their clients' products. While larger companies can afford to employ full-time UX designers, many other companies prefer to outsource the work to a UX agency. UX agencies are excellent for when you lack sufficient UX experience or know-how in your team.