I am just curious, so take no offence
Why would someone do that ?
None taken... So, by destroying a particular number of coins/tokens which can't be recovered, you are essentially preventing a proof that no one, including yourself can do anything with it. In my case, I'll be selling tokens and the remaining tokens will be destroyed on the blockchain. That way, no one can say I plan to sell them later. The proof of destruction is on the blockchain. It's often called Proof of Burn.
In my particular case, I wanted a vanity one that reflected the proof of burn was related my project.
https://en.bitcoin.it/wiki/Proof_of_burn