usb power for permanent installation

I'm setting up a permanent installation using an arduino uno. Is it safe to power it continuously via usb? Or is it advisable to use a 5v power adapter?

The reason I want to use usb is it means I only have to cut one hole in the enclosure rather than two.

btw sorry if this is in the wrong section.

What's the difference? USB power is 5V, so you don't have to add a regulator to your project. I've powered projects through a USB adapter (aka mobile phone charger) before (albeit with 3.3V regulator as the ESP8266 runs at 3.3V). Worked great.