Echoing everything @rickkas7 says. May not be worth effort/complexity to sleep the fuel gauge. Any impact on accuracy could overwhelm the minimal power savings. If you’re making any decisions on SoC (like when to service a unit) probably best to leave it running for max accuracy.
That said, after waking the fuel gauge from sleep it will use the last known SoC as its current estimate. As it continues to run will refine the estimate to converge on actual SoC. I haven’t tested how long it takes to converge and not immediately apparent from the datasheet. Could be milliseconds, seconds, minutes, etc. But if you are waking and then immediately reading SoC you might not be allowing time for update to current conditions. Experiment with leaving the fuel gauge on for longer before grabbing your SoC estimate.
Also, quickStart isn’t necessarily a super-secret command to get a quicker estimate of SoC. It just resets the SoC estimate and starts from scratch which could actually be worse than just leaving well enough alone.