The Crisis Commander is a rather broad subject. He can be run in a variety of ways, forming a lynchpin or a spearhead for your army. With access to all of the equipment a Crisis Suit can don he can fill almost any role given to him.
Today I'll be focusing on Commanders with the Positional Relay; a game changing device that can manipulate your reserves and thus give you unprecedented control of the battlefield. Flip open your codices and take a look at the Positional Relay and its abilities. It allows you to call in a single unit on a 2+ from reserves, denying all other reserved units from coming in that turn. This helps you in two ways:
1. You will (almost always) get the right man for the job at the right time. Whether it be a unit of outflanking kroot, a piranha squadron to wall off the opposition or bust a tank, railguns (either of the Hammerhead or AdvSS Broadside variety) marching in on the other flank to hit side armor, or deepstriking suits, you are almost assured that the unit will arrive right when needed.
2. On the exact opposite end of the spectrum, the Positional Relay can keep your reserves off the table. This is useful for players who use minimal troop choices; your valuable scoring units are kept off the board until late game when they sit on an objective. You can also keep your entire army off the board (save the Positinal Relay user) to lower the sting of drop pop or daemonic assault armies; half the army drops on a cheap unit in a corner, allowing you to outmaneuver him when your reserves come on elsewhere. This tactic is called Ninja Tau, and while useful sometimes, is prone to random fluctuations based on the insanity of reserves, and a good opponent's ability to pick you of piecemeal as you send in bait units turn by turn.
An example of a Positional Relay army would have powerful Heavy support options on a flank with a Crisis Team with Positional Relay. They would draw opponent's units across the diagonal towards a faux firebase, as they take heavy fire. Second and third tur reserves would slow or bother the units trying to reach your firebase, forcing the commitment of more resources. Your reserved Troops and a support unit or two come on the side they abandoned, landing on softened or deserted objectives late game, in a similar way to Fritz's (PLEASE look him up if you haven't ever heard of him) Eldar Jetbike Contesting/Capturing.
The great part about this is that if your opponent sits on the side of the board with the objectives and ignores your firebase, he is looking at massive Rail, Missile, and ranged Plasma fire hitting him as he hunkers down, which does not bode well; Tau are second only to the Imperial Guard at removing entrenched units from a range.
Those are the basics of Positional Relay tricks. Next up is the Commander's Bodyguard; a look at if they should be taken, and how to equip them.