Questions re using BNB to pay for transaction fees?

I'm a bit confused about using BNB to pay for transactional fees, and have some technical questions:

1. Does BNB need to be held in the spot wallet to do receive the BNB reduced transactional fee? Or, if it is staked, or stored in the binancw vault, can fees also be taken from here?
2. Does paying for transactional fees with BNB only happen of you're trading a token paired with BNB. For example - BTC / BNB? Conversely, if I were to trade ETH / USDT for example, could I pay a reduced transaction fee via BNB if I hold BNB in my wallet (or vault - see question 1)?