It would be impossible to list every reason anyone has ever wanted to upgrade their deck, but there are a few common ones. The bottom line is, like any other home renovation, the process is designed to make your life better. To that end, it's always a good idea to discuss honestly with your contractor what you want to achieve with the renovations. Whether you want to incorporate a design feature that reminds you Grandmother's old deck, or a cosmetic aspect you like about a friend's deck, or simply want more space, your contractor has likely worked with similar reasons in the past and will know how to incorporate your vision with building codes and safety features to design and build a beautiful deck for you and your family.
Convenience for Your Family
Ultimately, convenience is the underlying reason for any deck upgrade. If your family likes to cook and eat outside, you may want to add support and a permanent grill which runs off your gas line instead of a propane tank. If you spend a lot of time outdoors during the day, you may find extra sets of steps provide more points of access to the yard. Planters can be added, or customization built to accommodate the hobbies you like to engage in while on the deck.
Adding Value to the Home
Decks are an integral aspect of a home's value. However, some contractors when building a new house don't put much thought into the deck other than what is required as a basic part of the house's design. There is nothing wrong with that and there are reasons for such an approach when building a new house without a specific buyer in mind, but that doesn't mean you have to settle for a small generic deck once you've moved in. As with most improvement projects it may depend on the specifics of your situation, but usually an existing deck structure can remain while being extended or upgraded.
Maintenance and Repairs
When an older deck needs maintenance or repairs can be a great time to implement the changes you've casually wished for over the years. It's likely the deck has served your needs, but you always wanted it to be a little bigger, have built in seating and planter boxes, or any number of alterations. The perfect time to add those upgrades is when the contractor is there providing the required repair services so the replacement aspects can incorporate the design of the new features you've always wished were there.