Pros
There's really nothing more rewarding than helping someone achieve their dreams. The admissions letter is great, but the process itself is also very rewarding - helping someone uncover their story, think about their values, and really discover what they want to do with their one and only life - it's intrinsically motivating to be a part of that journey.
Cons
Clients can VASTLY underestimate the amount of effort and time that it takes to craft all the elements of the application package. As an advisor, this can be frustrating and you may have to work late nights / weekends / during a holiday break to make sure they get back on track. It's all a part of the process, but new advisors need to be aware of this tendency for clients to overestimate their bandwidth. As long as you plan around it and get your clients to understand the urgency, you can mitigate this risk.