If you are not familiar with using a gimbal your moving shots are probably not as steady as they should be unless you have the worlds steadiest hands. But if you are human, a gimbal will probably really help you achieve the fluid motion you want in moving shots. They are particularly useful with small camera like a GoPro due to the vibration often associated with the kind of situation and are also often used for DSLRs to get more professional looking shots.
But you can also use a gimbal on a dolly to help smooth out any motion that may be caused by the rig itself. If you take a look at some professional camera rigs they are using a gimbal in their setup as well. Another excellent situation to use a gimbal is when recording with a GoPro on a car. The uneven surface of the road can cause a lot of vibration and jolting in the video
You’ll need to do some research for your specific kind of camera because not all gimbals are a ‘universal’ fit. Some are made for small point and shoot camera or GoPro, some for DSLR and others for larger movie camera. If you are looking to buy one for a DSLR expect the prices to start in the $400-500, and if you are looking to buy one for a video camera be prepared to shell out well over $3000. They are expensive pieces of equipment but well worth the investment due to the quality shots you can get.