This usually means waiting a few weeks after the deck is completed before sealing. Many people never treat and seal their decks. Untreated decks don't fall down or rot away quickly. Nothing dramatic happens. They will simply get dirty and the surface will become much rougher much sooner.
Splinters are a common problem with wood decks.
Another hazard is slick surfaces. Just like the algae and moss that grow on rocks next to a stream, the organic material growing on a deck can make the deck very slippery when wet. Cleaning and sealing a deck kills, removes, and slows the return of organic build-up. Approximately once a year, the deck should be checked for loose boards and protruding nails, thoroughly cleaned, and resealed. Cleaning involves the removal of dirt, algae, moss, and other organic matter.