There is nothing in consensus rules that says you must pay any amount in fees. But a zero fee transaction may not be likely to get mined. A less than 1 sat per vbyte transaction doesn't have to be zero fee, though.
Your transaction might be 306 vbytes. If you pay 1 sat per vbyte, the total fee would be 306 sats. If you pay 15 sats per vbyte, total fee is 4590 sats.
If you pay 0.5 sats per vbyte, total fee would be 153 sats. You still pay a positive fee, just it's less than 1 sat per vbyte.
Only kinda related, but Bitcoin Core 29.0 adds support for ephemeral dust, where you create a single dust output, but only if the transaction has no fees.
I ask because sometimes thinking about dust transactions. If it's possible to add them to the block all the dust will eventually get back to circulation. In this case all sats really matter
Would it be fair to say a free market decentralized allows for players to play. And this is when a player spots an opportunity to exploit a new direction away from the pack.