XFCE: using startup notification
 

I saw the option "use startup notification" for any applications I add to a launcher in the XFCE panel. I looked that up and found that "use startup notification" means "the window manager will show an hourglass while the program is loading."

The thing I don't understand yet is, why would I care about that? The only benefit I can see is that it's one way to tell whether the app is frozen (the hourglass stops spinning). I used to find that benefit in the aquarium icon that the MEPIS panel used to offer, about ten years ago: if your system ever froze, you could tell from the aquarium not moving anymore.

Besides--now that I think of it, the application I was adding to a launcher, Leafpad, runs so fast that it has no time to display an hourglass.

It can be useful to show that the application is opening and you have selected it properly if the application is one which takes a while to open -- I notice that Icedove (Thunderbird) takes a fair amount of time to open with a few email accounts, for example, and the hourglass stops me wondering whether I clicked it or not.
So, no, it's not really that important.