A short answer is that it is "just different". It's another way to tweak an existing LLM to do another task, without having to finetune the whole system. Conceptually, this way is simpler than LoRA and seems to work as well or better.

In the paper, the authors mention that one advantage is that you can use this technique to add new modalities. The whole method works by adding to the prompt at the top most layer(s), so you can add not just words, you could add tokens that come from an image. They have an example on the top of page 4 with a picture of a baby opening a door.