Quote Sentinel only notifies you -- at the time the first Quote Sentinel script was written, I couldn't find something that would send me a text message when my limit was about to be triggered.
Basically I personally had 2 main use cases:
1. I want to go to lunch and I want to be notified if something is happening and I should come back to my desk.
2. Markets are dynamic. Today I'd love to buy AAPL 10 bucks lower than it is, but if the market drops like a rock, it might not seem that great anymore. For big moves, I'd rather be notified so I can make a decision with the new information instead of my limit/stop getting filled based on what I thought was a good idea before.
Its definitely not an app for everyone, but it solved a specific need for me so I thought it'd be worth turning it into an app for others.