That’s fine if she didn’t need the money. Many took the stimulus money who didn’t need it.
Many find it worth it to spend 30 minutes filling out the FAFSA to get some money. You didn’t. OP asked what the benefits were and I gave one example of a benefit that her children could possibly get for just filling out the FAFSA.
Also, at the beginning of when my kids went to school, the high school or school district was getting a benefit if all their students filled it out. Michelle Obama traveled to several schools in Florida and ‘helped’ students fill out the forms or had a big drive and schools that had a high percentage of students fill out the FAFSA, even if they weren’t going to college, got something. I’m sure the Obamas didn’t fill out FAFSA for their kids, but they were sure encouraging everyone else to do it if eligible.