Specific gravity is the heaviness of a substance compared to that of water. Water being at 1.000. Anything higher than that (water) will have a higher viscocity.
If one beer finishes at 1.023 and another finishes at 1.010, the beer that finished at 1.023 will have a higher viscocity and therefore fuller mouthfeel.
When I make an IPA that finishes at 1.016 vs another that finishes at 1.010, the higher finishing gravity will lend more mouthfeel than the lower gravity.
This is what I have always known to be true.
Here's some data to show what I have just explained.http://www.csgnetwork.com/sgvisc.html