There are a few things i enjoy sharing on Google Maps, the first has to be pictures and second is probably adding small businesses. Adding pictures allows other users to make up their own mind about a place rather than read a subjective review. I personally rely heavily on pictures when i am looking up a place, be it a restaurant or a touristic site.
As for small businesses, many of which do not have any online presence, i like to add them on to Google Maps to make it easier for other people to find them. I usually stumble upon these places by chance or sometimes by actually physically looking for such shops door to door in a market. There is also a selfish aspect to it i guess as it makes it easier for me to navigate back to these places in the future.