I'm using this on my desk to mix 4 3.5mm devices - some devices that have really strong headphone outputs will be fine with this device (e.g my iPhone output was still good and loud).

But it is a very useful device.

However, if you are in a situation where you have 4 computers or other 1/8" outputs and want to connect to a single set of speakers, this is a great device.

This is a passive device and it will absolutely produce lower sound than if you had a device hooked up directly to speakers.