When you install an OS X application from a .dmg file, it is very typical, when you mount/open the .dmg, to see the application's icon followed by an arrow pointing to the "Applications" folder, a bit like this:
CoolApp => Applications
Hinting you that you should drag & drop the application into the Applications/ folder.
However for a lot of applications, like Skype, you can just drop it anywhere you want, like on your desktop.
For some application, you're not even forced to enter the root password of the system. Yet even these application typically suggest that you drop the app in the main (system wide) Applications/ folder.
Besides making the application available to all users (which isn't that great an argument on systems having a unique user account), what else am I missing if I'm simply installing the application in some folder of a regular user account (that is: not system-wide)?
I guess my question really is: are correctly designed OS X application guaranteed to work even if you do not drag them to the system-wide Applications/ folder?