Did you see that short piece in the weekend paper about sealing projects? It said the edges are the most common spot for sealant to peel up. They stressed that cleaning there is not just a quick wipe but a needed step. It made me remember when my own kitchen tile job went wrong from a dusty grout line. Giving edges a good scrub really does make all the difference for how long it lasts.
You're right about giving edges a good scrub, but I learned the hard way that even a tiny bit of moisture left there can ruin the seal. When I sealed my bathroom tiles, I scrubbed clean but didn't wait for them to dry fully, so dampness got trapped and it peeled in weeks. Now I use a hair dryer on low heat to make sure edges are bone dry before sealing. It's an extra step I never see in guides, but it's key for making things last.
Scrubbing edges clean does help, but if they aren't completely dry, the sealant can still fail quickly. David_foster25 had a good point about using a hair dryer to avoid trapped dampness. Getting both the cleaning and drying steps right is what makes the seal last.