Is there any functionally relevant reason to get it?
All depends on how quickly you adjust to doses of adrenalin...
I'll tell you why I went with it originally (besides enjoying fast/quick vehicles). One of the dirty little secrets about almost EVs, is that all the performance stats they quote you are under ideal circumstances which have things that need to align to get the stated performance that you might not be aware. This is not even accounting for production variations.
Let's list 2 of the key things that can easily impact your acceleration times.
- Battery pack charge level
- Battery pack temp
You'd be surprised (until you understand it) how much these 2 variable can impact your acceleration performance. Unlike a ICE engine, the performance usually varies as your "fuel tank" runs dry. With an ICE car, less fuel in the tank doesn't hurt the engine's performance and as the tank empties, less weight helps the power to weight ratio. All times Tesla, or other EVs companies list, for acceleration runs are with the battery pack at, or very near, 100% charge. As the charge level goes down, the performance starts to fall off.
If the battery pack is not at the optimal temp, it can't provide all the power it is capable of even if 100% charged. When battery temps are not optimal (usually when too cold), they can't deliver the energy as fast as the motor can use it, thus resulting in reduced acceleration.
So take a cold day, cold battery pack, at 50% charge and now your M3 Long Range (LR) won't do 0-60 in 4.2 seconds. It might have turned into a Model Y Long Range and now runs 0-60 in 4.8 instead. We don't want to charge to 100% all the time for battery chemistry in the Long Range models as it is bad for degradation. As a result on the street, you will almost never see the claimed times in most of your driving that Tesla advertises.
I like to call those times, and seat of the pants feeling, the "freshly charged feeling." The car just feels a bit zipper and sharper when you hit the throttle. As the charge level falls off so does the fun.
With acceleration boost, I basically have the freshly charged feeling all the time when compared to the stock LR. I could be at 50% charge level with a boosted LR and have a cold battery pack (but not frozen) and it will still outperform the stock LR. That is why I love boost. I still have a very quick car no matter what the charge level. Even at 75% charge level, my M3 LR ran 0-60 in 3.73 second with no rollout. The battery pack was at about 50F too. Not exactly optimal temps.
Compare that to stock under ideal conditions of 4.2 seconds. You WILL notice the difference. For the time I had it full charged for a trip and a warm pack, it had an even fresher charged feeling.
That is why I love the boost, no matter what the charge level, it is an absolute blast to drive.