The downsides is that this makes the bottom of the case quite hot on a place you can touch, but putting a plastic hardshell over the entire laptop deals with that, and also gives protection.
> a longer maximum performance before throttling.
As implying that the purpose is to increase the thermal mass, not necessarily the dissipation. It should still be able to reach maximum performance for longer, it will then just also take longer to settle back down again.
Performance numbers reflect the optimization. I personally haven't done it for fear of affecting the battery lifespan (and possibly other components' lifespans.)
Really hard to resist due to its simplicity and noticeable improvements.
Is the added plastic shell case a "bandaid on a bandaid" sort of solution to deal with that heat? Absolutely. But you might want that case anyway - I've had several laptops that would have had broken screens or were yanked off a desk by an attached cable and survived by the sacrificial plastic shell taking the impact.
Like all things, it's a tradeoff to consider.
I still have pads left over from trying my damnedest to reduce fan noise on a Dell XPS. Used pads on every hot stop and didn't help.
If I were to need any more performance I'd just swap it out for a newer MBA or a MBP with a fan.