When I play Super Mario 3D World, I get an extra life for every 100 coins I've collected.
In Bowser's Fury there are also plenty of coins I can collect. But I don't see a counter for Mario's lifes. So what is the advantage of collecting these coins? When Mario dies, of course, the amount of coins is reduced. But it seems: never to 0 coins.
Coins don't have as important a purpose in Bowser's Fury. You will lose coins if you lose a life, as you noted, but it will never go below 0.
If you do collect 100 coins, you will be given a random power-up. This could be one of the power-up options that you can collect and use later (mushroom, cat bell, leaf, boomerang suit, etc.), or a super star. And like all Mario games, collecting 100 will bring you coin count back to 0.
