Why would someone tend to use a high-side device instead of low-side device?
If your load is referenced to a system ground, putting a switch in series with the low side can result in a ground potential difference proportional to load current.  (Load * RDSon)

This can erode noise margin on digital signals and inject noise and error into analog circuits.

To get around this, high side switching is often used.  You can use a P-Channel FET for this, or develop a supply that's high enough above the rail you are switching to fully enhance an N-Channel FET.  

For the same RDSon, the N-Channel FET will be cheaper than the P.

You can use a charge pump, develop an auxiliary supply to drive the FET gate.  Some integrated load switch drivers have a charge pump built in and provide other useful features.

There are also integrated high side load switches that can be useful for certain load ranges.  Here's an example from Micrel:

Micrel Driver