I commute to work by bicycle every day, and I have several bicycles to choose from depending on weather and load capacity. Out of all those bikes, I have two that I use regularly, one for fair weather and the other for foul.
The foul weather bike has the most load carrying capacity, and that's the bike that I use the most when out shopping, and the remaining bikes that I have are either setup to serve as backups for the first two main bikes or can be used as guest bikes.