A sliding saw is an overkill, and we actually don't recommend it as it is typically more work. For normal cuts, a non-sliding miter saw will do for speed. For large boards such as 2x12 - rafter square + circular saw is easier. In the video, they say:
"We tackle how to make straight cuts with a circular saw. This covers accurately making cuts without having to use a miter saw. After all, many times the wood you need to cut is right there on the pile. We find it much easier to bring a circular saw and rafter square to the material. We know this is a basic tip, but for those just starting out, it might save you a lot of time, money, and even improve your cut accuracy. Grab your favorite rafter or Speed square and follow along!