To be honest, I don't think I've ever used the services tools on my Mac. These are, you know, accessible by clicking on File in your menu bar. Services were set up by Apple to do specific actions with elements inside an application. ThisService will appeal to those that have some programming language as it allows you to write up scripts which you can launch in the services part.
While actually writing script is probably the hardest part, using ThisService is accessible to anyone. You'll be able to load your script directly from the interface and choose whether to have it act on input, produce outbut or filter (do both). ThisService lets you set a menu shortcut and include both a copy and reference of the script.
ThisService will certainly appeal to people with at least a bit of programming language, allowing them to customize their services section on their Mac.