FAFSA/CSS is just one part of it. The main part was matching kid with schools based on grades, ranking and desired degree as well as where they have the best chance for academic scholarships and then you can focus on where to apply. They also review all essays and applications before you submit them - no way my kid would have listened to my thoughts/comments on what was originally written so having an outside reviewer made a big difference in what was originally written by my kid vs what eventually got submitted...
Also, if you fill in the FAFSA incorrect and you have to wait a full year to make corrections. There are a lot of grants and other scholarships available - $500 here, $1000 there - that all require a FAFSA when you apply for them to even be considered.
They also help you "negotiate" with schools who are offering you scholarships - school X may initially offer some amount while school Y makes a different offer. You can play one offer off the other to get even more money if they really want your kid especially if both schools compete with each other for the same pool of students. Our advisor has a good database from previous clients so they have a good feel of how much the schools are willing to pay/increase their initial offer.
Sure, you can do it all this yourself but I hire consultants all the time in my line of work and understand that sometimes it's worth hiring someone who does this process all the time vs. trying to figure out how do it all by yourself...