The obvious benefit is it will save you time. You engage a recruiter to do the initial grunt work of identifying suitable talent and that is not as easy as it sounds.
Recruiters have spent years developing their craft to identify talent in certain sectors and have techniques to attract hard to find candidates. They are also independent and can often nurture talent to consider your role - it’s not a simple exercise, why would someone in a good company in a secure role consider your company if you are a start up, for example? Have you got the time to nurture that person? What if you are a ‘name’ in your sector, is it enough just to use your prowess to attract new employees? Not always.
A recruiter will consult with you to understand how they can portray the benefits of working for you (whether you are a start up or a major player) and independently sell those benefits of working for you. It’s unseen time and effort that goes on behind the scenes - you may only see the output in a CV (and multiple layers of assessment and evaluation) but this is the real benefit of using a recruiter - they know the people you need, often before you know you need them.