I struggled with this while packing for my trip this month. I have a Canon SL1, which is a very small DSLR. It takes great photos, and my phone is a little older and doesn't take photos of anywhere near the same quality. I have a couple compact pancake lenses that actually make my DSLR lighter in weight than my point and shoot I used to use. It's so light I can forget I'm wearing it.
The thing is, I've taken TONS of photos at WDW with the camera. Ride photos. Park photos. Resort photos. You name it, I've snapped it. My laptop is overloaded with WDW photos!
The weather forecast is a little rainy, which means I probably would not want to take the good camera to the parks every day. Plus there is so much construction going on right now, that I don't need photos of. So I decided not to bring the camera on my January trip. I may take my iPod into the park with me, as it has a better camera than my phone does, just in case I come across something interesting.
I make this decision each trip based on the criteria for that trip. When I go in August, I anticipate that Toy Story Land will be open at DHS, and I will want good photos, so I will be taking the camera on that trip. I took the camera on my December trip to get photos of the Christmas decorations as well. I just don't think it's needed on this particular trip.
You don't need to bring your camera. It just depends on whether you feel you will want photos other than the Photopass and phone photos, and whether your phone is up to the challenge of taking photos everywhere you might want to.