Laptops with a dedicated GPU generally use some switchable graphics technology like Nvidia Optimus or AMD Enduro, mainly to increase battery life as dedicated GPUs aren't nearly as optimized for efficiency as integrated ones. In practice that means that the laptop display is directly connected to the integrated graphics, but the dedicated GPU can still be used to render things and route them through the integrated GPU.
If you don't use an application that can make use of the dedicated graphics card like games or other graphically intensive applications, or want to use the GPU for compute workloads I would stay away from laptops with a dedicated graphics card, they only make the laptop heavier, thicker and more expensive and can drain the battery.
Integrated GPUs nowadays are more than capable of doing everyday things like video decoding and basic animations, they are often even fast enough for some light gaming and can run many older games just fine.