Yes, it's used normally to hide an application into the system tray.
Usage from the author's website:
It's really useful because many programs don't provide the funtion of "minimize to the system tray". Currently I use it to hide the opera in my system tray and it works!
TrayIt! runs on Windows 95/98/Me, NT/2000/XP/Vista and does NOT require any installation.
Simply create a new folder and place TrayIt!.exe and TrayIt!.dll there. When started, TrayIt! will show a dialog box with a short explanation how to use it. You may choose to load TrayIt! on system startup by selecting "Option" and checking "Load TrayIt! on StartUp" box.
You can temporarily put any window in the system tray by keeping down the
button when minimizing the window.
To always keep window in the system tray when minimized, click with the RIGHT mouse button on the corresponding icon created in the tray in the previous step and check "Place in System Tray" in the popup menu.
Clicking with the right mouse button on the minimize icon will bring TrayIt! context menu for this window. Just check "Place in System Tray" in the popup menu to make window always go to the tray.
Please note that context menu will work only for the standard minimize icon and will not pop-up if the program use skins like MS Media player.