The mitre joint is similar to a butt, but marginally stronger and has much greater aesthetics compared to the butt joint. The reason this type of joint is stronger and more aesthetics than a butt joint is because the 45° cut at the ends which are clued together. This provides a better surface area for adhesive to be applied while also hiding the end grain giving it a nice finished look.
The cuts are better achieved with a drop electric hand saw, which will give you finer cuts compared to a hand saw. This joint is very common on picture frames because no end grain shows and they don’t require much holding strength