It’s just a seatpost inside another seatpost right, how bad can it be? Or is there something I’m missing?

I’ll throw in my own conclusion:

Yes, but if you saw off too much you will take out the pins that stop it from twisting.

I’m not quite sure why said pins are needed in the first place – I find the post doesn’t twist (even within the small amount of play allowed by the pins) when the clamp is done tight anyway. So sawing off above the level of the pins might have consequences, or it might not.

I guess if you got a bit extreme you might mess up you minimum insertion depth. What’s the matter? Tiny Seat-mast?

After a certain amount of cutting it will cease to be a Scoper and end up as a heavy shim.

Agree with you apart from the bit about me having a tiny seat mast 😉