A PDU (Power Distribution Unit) is a device for remotely switching power to connected equipment. It enables to you activate, deactivate, or reboot your gear without driving all the way out to a remote site. It's a fairly simple box with an array of relays that can toggle electrical power to individual devices.
Imagine the difference that could make, especially for distant sites. In certain parts of the world, your sites might be under snow for much of the year. The more difficult it is to get to a remote facility, the more important a PDU becomes.
PDUs can support various voltages
Some PDUs are built for use in corporate IT environments where the power is mostly 110v AC (at least in the United States). Others handle -48v or +24v DC. This affects not only the needed circuit design but also the connector type that you'll need. Make sure that, whatever power voltage you plan to use, your PDU will accommodate it.
PDUs come in various form factors
Just like any piece of equipment, a PDU should be sized to fit the environment where you'll deploy it. If you don't have room in your equipment racks (or your deploying in a small or unusual location), you may want one that mounts to the wall. Some designs run down the side of an equipment rack without consuming any of the rack space itself. Finally, for rugged industrial environments, rack-mounted PDUs are standard.
You should control your PDU using the method of your choice
Good remote monitoring and control equipment works for you - not the other way around. If you only have a few remote locations, a good built-in web interface will let you toggle inputs and outputs when you need to.
Once you have more than 10 sites or so, that strategy breaks down. You need a centralized interface to manage your PDUs. That should be the same master station you use to manage equipment and environmental alarms. If that happens to be an SNMP manager at your company, make sure you purchase PDUs that can be controlled using SNMP SETs.
Make sure you choose a good manufacturer
Because PDUs don't generally require incredibly complex logic or processing, some vendors end up selling PDUs that really aren't reliable. Maybe they're tough to use. Maybe they're not compatible with open standards. Maybe they won't last very long in harsh environments.
Your network is serious business, so you need to choose power distribution units that will support it properly. As you interview potential vendors, ask how much experience they have. Demand to see references from previous happy customers.