Travel agent here. I echo all of what Breeze stated. Most of the below more applies to those traveling out of the country. I do very little US travel.
Obviously I would advocate for using one, especially if leaving the country. We can almost always meet the pricing you see online, many times we can beat them. This is not always the case, but usually can come close.
Agents are well-versed in the ever-changing rules, especially with COVID. We spend countless hours on hold to make changes/updates to your vacation. Within the past month, I have spent over 50-60 hours just on hold. This past Sunday I was on hold 7 hrs 21 minutes before an agent picked up - all for a 3 minute phone call.
We know which resorts to send you to, and which to avoid. We are in groups with thousands of agents and we hear all the feedback from the various resorts. When something goes wrong we have a team of people who can try and get issues addressed, not a single person trying to get a resolution at a resort.
As far as your points/stays - I will say it depends how the trip is booked. Yes, if we book direct with Marriott, Hilton, etc, you will get your points. If we bundle flight and hotels (like with AA Vacations), those do not always count. So you would need to know which is more beneficial to you.
I like Breeze do not charge fees. Many agents are starting to so they don't get tire kickers. To me this is just part of the service provided - all of my quotes and services are free of charge. The only exception is if I book flights only, which is not my favorite thing to do and I most likely will no longer be doing this after some of the crazy stuff that happened during COVID.
Just want to add you cannot go wrong with a stay at Le Blanc Cancun. I was there back in October and it is absolutely stunning.