Not to brag but for credibility - I race in a very competitive amateur series and can turn in laps within 0.2s/minute of my pro coach, who is an active pro racer with numerous wins. I review data after practically every day of driving and log everything up to the individual wheel and tire temps and corner heights under load, and generally know what each metric means for car setup or driving technique.

Here is a summary of ABS on track based on everything I've learned so far (applies to the 991 or newer GT3 ABS - older ones were not as good).

1. In a straight line and steady state, ABS will stop the car faster than a human, even at threshold-braking. Getting into ABS during straight-line braking will be the most efficient way to brake. It's easy to prove by data. Even if you can perfectly put the pedal pressure at just before the lockup level (most people can't - they just brake too lightly so ABS does not engage), the problem is that grip changes and the balance of grip between axles changes over time, triggering ABS & EBD. So completely avoiding ABS reaction inevitably means that you are leaving braking force on the table. But there is a catch.
2. Engaging ABS has a cost - brake pads can wear faster or even crumble if worn/overheated due to vibration, and can also leave uneven deposits - many have seen multiple overlapping "stamp imprints" of a brake pad on a rotor - that's typically what a result of ABS action with overheated pad looks like. It may cause vibrations and uneven braking in the future.
3. You do not want to engage ABS during weight transfer. For example, if you slam the brakes so quickly the front wheels start to lock up before the weight transfers to them, ABS will engage prematurely and not allow full brake pressure to build up, which will reduce deceleration and delay the weight transfer, creating a kind of a negative feedback loop.
4. Always make sure you are out of ABS sufficiently before the turn-in point. The problem with ABS is that it prevents knowing exactly how far beyond the threshold you are - you could be pushing the pedal 1% stronger than threshold or 50% - it will feel the same. And when you start turning in and gradually releasing the brake, you need to index the brake release from the threshold. Let's say you know you need to be at 60-70% of the threshold the moment you start turning in. If you are in ABS, you will have no idea whether you need to reduce the pressure by 30% or by 60% because you cannot feel how far past the threshold you are pushing into the ABS zone. So it's important to be out of ABS and feeling the brakes before starting to blend braking and turning, and not get into ABS while turning (that usually just does not work well, too long to explain why).
5. Some anomalies of track surface can make ABS suboptimal even in the straight line - typically it happens when one wheel gets very unweighted or in the air, so it does not provide braking force, and that creates a force that rotates the car (on one side two wheels brake but on the otherside only one). ABS/EBD will try to compensate for this force to avoid rotation or spin, but that may be counter to the driver's intention. In such cases I would not go into ABS if possible or turn it off. But if that happens, you will know exactly where it happens - it's noticeable.

So, unless there are special circumstances, I would drive an ABS car like this:
- Quick but gradual brake application, making sure ABS does not engage before the weight transfer completes (it is very quick, though in the 992 generation and especially in the RS)
- During straight-line braking, feel free to (gently) dip into ABS for best performance (unless brakes are starting to get greasy due to pads overheating). If anything, it's a good way to understand where the threshold is - otherwise, how will you know? In non-abs cars, racers slightly lock up wheels during warm-up to know, for example. In ABS cars, you dip into ABS.
- Before turn-in point, make sure to release brakes enough to not be activating ABS, and releases brakes during trail-braking quickly enough so that ABS does not kick in then either.
- If there is a specific place where ABS engages unusually early, try the threshold braking there and see if it's better.

Some other caveats:
- Stability control sometimes vibrates the brake pedal too, so vibration can be not ABS but stability control. You do not want that type of vibration.
- Long ABS engagement feels like brake fluid overheating - pedal becoming soft and going toward the floor. That's ABS reducing pressure rather than fluid overheating, although it feels very similar. ABS does not put more heat into pads or rotors but can have a similar negative effect on brake feel when overused.