SYS cap is always draining at a constant rate when your shields AREN'T full - that is when they're recharging at all. Counter measures such as chaff also utilise a small amount of SYS energy.
It's only usually a problem when shields go down, as at this point the shield generator starts taking increased amounts of energy from the SYS capacitor to make the shield reach 50% quicker and be available to you sooner. So this is when you'll generally notice the drain, as 2 pips to SYS at this point usually isn't enough charge to fully counter what is being drained.
An all-round charge enhanced PD means that even with broken shields you can sustain SYS energy on less pips, and if it's running down because you took pips out of SYS, you'll get energy back into the capacitor faster. If you let the capacitor run out that's obviously bye to shield recharge and countermeasures.
Realistically how useful? Well in many engagements you'll be running at least 2 pips to SYS, often 4. Extra recharge on SYS is therefore nice but not a game-changer. However, the extra recharge to ENG for boost is always useful, especially as in many PvP or otherwise intense engagements you'll run 4/0/2 on pips and want as much boost recharge as you can when you do put pips back to SYS. Remember also that all-round recharge can go up to G5 whereas the area specific upgrades only go to G3. Given recharge is frequently more important to DPS than capacity, it's arguable that the charge enhanced mod at G5 is just as good for your weapons as weapon enhanced anyway, so it's pretty much a no brainer as far as I can tell.
Grats on the roll btw.
EDIT: The above assertion it isn't a game changer largely assumes a mid to large sized ship is in the mix. For ships such as the iCourier with a small distributor, it's a game changer pretty much all round. With shields down smaller ships can run into fairly serious micro-management of pips mid fight to avoid the shield becoming effectively dead. Charge enhanced will give you a breather here and allows the use of bi-weave shields in PvE (cannot recommend bi-weaves on an iCourier in PvP any more
) without watching the SYS cap drain faster than red wine at a cougar convention every time it breaks.
