In a nutshell, poke charge and poke cancelling is just a simple variation of shield charging and shield cancelling, but with subtle advantages and some slight trade offs over the traditional shield charging/cancelling.

In order to efficiently use poke charging and poke cancelling, you will need:

~A battle sprite that doesn't listen to your commands~

Essentially, it gives players who have poor connection to the server (or in some specific cases; server lag due to an event [cough- cough- Apocrean Event cough-]) the ability to spam the "give my sprite a command" aka the "poke" animation without actually activating said sprite ability.

Important Note:
It is vital that the sprite doesn't use an ability as you would be spamming the poke animation in order to initialise poke charging and poke cancelling. Once an ability is used, it is impossible to poke charge/cancel for the duration of the ability cooldown.

Like I said previously above, poke charging/cancelling is just a simple variation of shield charging/cancelling.

Replacing shield charging for poke charging:
You simply replace the "hold shield, then hold attack, then release shield" into shield charge with: "press button to poke, hold attack" into poke charge.

Replacing shield cancelling for poke cancelling:
Use the "poke" instead of shielding at the end of an attack.

Advantages of "Poke Charging" comparing to shield charging:
~ No reduction of movement speed
Haven't you noticed that when you activate your shield for a shield charge, you reduce your movement speed?
With poke charging, there is no reduction in movement speed thereby increasing evasion. Additionally and although, the potential distance gained from poke charge compared to shield charging is only a step or two, over the course of 10 - 20 chain charges (for example, in an arena or SL) that potential distant gain from your chain poke charges could mean the difference of evading an attack or getting hit.

~ Bufferable attack command
Once you press the "poke" button you can buffer your sword charging by holding attack before the poke animation finishes.

~ Very consistent
It is consistent because it is possible to buffer an attack command before the poke animation finishes. What it means is that weapon charging will start on the FIRST AVAILABLE FRAME POSSIBLE after the poke animation ends.

~ Less button pressing
You need to do 3 things in order to initiate a shield charge compared to 2 things from a poke charge. Less finger hurts at the end of long fights.

~ No observable difference in time spent in setting up a poke charge compared to a shield charge
If there are any time differences, it would probably be in the single digit milliseconds.

Disadvantages of "Poke Charging" comparing to shield charging:
~ Cannot shield while poke animation plays
That is the only trade off for using poke charging, the temporary lack of ability to shield when setting up a weapon charge.

Advantages of "Poke Cancelling" compared to shield cancelling:
~ Bufferable poke animation and therefore very consistent
Before your weapon discharge animation ends you can buffer the poke animation by hold the "poke" button, thereby allowing the player to "poke" on the FIRST AVAILABLE FRAME POSSIBLE.

~ Very efficient as a cancelling technique for chain charge attacks
This is probably the strongest advantage that poke cancelling has over shield cancelling.
Here is the scenario; you charged your weapon up and released in onto a slag, the moment you release the weapon charge you buffer in your poke animation in order to poke cancel the charge attack. Then while the poke animation plays out (due to poke cancelling), you buffer your attack command and immediately initiate a poke charging and therefore start charging your weapon at the first frame possible. Rinse and repeat. As long as it is possible to poke continuously, you can chain charge attacks with ease.

Disadvantage of "Poke Cancelling" compared to shield cancelling:
~ Inefficient as a cancelling technique for normal attacks
Poke cancelling was never intended to cancel normal attack animation. Its strength lies in mass chaining charges.