If KH and Ravelry seem similar to you, keep looking! I would say the areas of overlap are very few. Have you looked through all the amazing FOs yet? Looked to see what others are doing with a yarn you have? (and maybe haven't selected a pattern for). Looked to see what problems others have had with patterns you are working on? Entered all your projects and planned projects? When I did this, I was shocked to learn I had 7 UFOs floating around. I was only aware of 3 that I was actively working on. Having them right there in black and white (since I don't take photos of WIPs), motivates me to finish so I can have that nice, shiny color picture to show off.
The queue feature helps me prioritize projects so that I don't start working on one thing, then realized I'd rather be working on a different project (well, as much as possible - I am still a bit impulsive!) And the favorites feature helps me keep track of things I love and want to remember for the future, but maybe don't want to make that exact project (like if I want to remember a unique neckline or colorscheme or that sort of thing). The stash feature helps me remember that I DON'T need more yarn, but also helps me justify new yarn purchases because I can be sure I didn't already have anything in that gauge/color/fiber.