Currently we are using logo for taskbar icon in desktop v5, where the size is definite fit for the purpose, but it may not designed for such scenario.
Logo could be rectangle, where favicon and icon is often designed to display under squared area. As long as the icon has enough size, we should try to use it.
Actually, the logo within portal is defined through admin portal. The logo used in desktop installation is purely for display. So technically icon can be used for both favicon and log.
Currently we are using logo for taskbar icon in desktop v5, where the size is definite fit for the purpose, but it may not designed for such scenario.
Logo could be rectangle, where favicon and icon is often designed to display under squared area. As long as the icon has enough size, we should try to use it.