Fat Bikes / Fatbikes

Cyclescheme;

Does the bike have to be used for commuting?

Employees should use the bike mainly for commuting to and, if relevant, between work places (at least 50% of the bike’s use should be for work purposes). However, the bike can also be used for non-work purposes and there is no need for employers to monitor individual usage or for employees to keep a mileage log. Please note that employees cannot claim business mileage allowance with a bike that is being hired to them by their employer.

layman's term; no one is telling you that you have to commute on a fat bike.

I however, would encourage you to do so just to hear the feedback you get from fellow commuters.