Are there any advantages to using s-clips for attaching a table top instead of a right angle bracket?
The clips that are used in the nightstand in the video are so the solid wood top can move. If the top is secured too tightly and when seasonal movement occurs it will crack. The slots in the apron that the video shows allows for the movement. The slots don't have to be all the way through, it just as easy while machining the wood.

There are other ways to fasten tops and still allow movement, slotted screw holes and there are washers that look like there are two together and look like a figure 8. One side attaches to the apron, the other to the table top. The clips in the video are available online, as are the ones illustrated below.