The biggest enemies of a wooden decks and other structures are Sun and Water.  If your deck is not sealed properly, water will enter through its surface, causing swelling. During hot weather, water in the wood evaporates, causing it to shrink. This swelling/shrinking process causes wood to crack and twist more than would occur with well sealed wood.  Sealers promote dimensional stability AND improve your wood's appearance.  Utilizing transparent oxide pigments like Sun Frog does also buffers UV Sun Damage and adds aesthetic color, too.  Decks and other natural exterior wood investments are are expensive to build and more and more expensive to replace so seal them when they're new and maintain their seals over time!   Your first year's seal on new wood is the hardest to get to last since the wood hasn't "opened up" for penetration of much sealer.  After the first year, repeat seals however, especially ours, should last 2 or 3 years before needing to be re-done.  Rule:  When sealing, apply as much sealer as the wood will take in ONE overall application (wet on wet if soaking in still is taking place), then lightly rag any excess and let dry 48 hours before using.  Good to go!