Imagine a situation when you want to withdraw you LP on Pangolin AMM which located on Avalanche and ran out of AVAX for gas fees. Or situation when you don't want to spend you ETH on gas fees for USDT<>UNI swap.
This situation can be solved by Gasless feature that will allow users to pay the gas fees in an asset they are swapping, in case of USDT:UNI swap you will be able to pay gas fees with USDT. This will tremendously improve user experience for users interacting with multiple chains.