The amount of RAM determines how fast your laptop can be 'fed' with work. You can have the fastest processor in the world, but if it doesn't have enough RAM to feed it the data to process, the computer will have to fall back on the hard drive/SSD for temporary data storage, leading to frustrating slowdowns.
There's really no downside to having more RAM, so buy the most you can afford. 16GB is a bare minimum when editing larger files, with 32GB being a safer amount for a future-proofed editing machine. And don't rely on being able add an extra stick of RAM yourself further down the line. Many new laptops have RAM permanently soldered in, so the amount you spec at purchase is the amount you're stuck with.