If you’re familiar with the floor press, this is a “bench” version of that, basically. If you’re not familiar with the floor press, it still is, but I’m going to tell you what the means
The floor press is a bench press done laying on the floor. The reason it’s useful is that at the bottom, your upper arms rest on the floor, which allows you to take tension off the pecs so you’re starting with zero elastic tension at the bottom of every rep. This helps work the muscles harder because of that missing assistance.