When I first started commuting again in 2008 my commute was less than 3 mi each way. That was sufficient for a few weeks. But I decided to up my overall mileage. So I started going for 4-5 mi at lunch and made the ride home last 5-6 mi. At the time I was riding a 90s Raleigh MTB.
In 2010 my bike was stolen. I bought a Trek FX 7.1 hybrid. The same year my work moved and now my commute was ~5mi each way. In a way this was nicer. Because I don't feel like I HAVE to extend my ride home. I can if I want to but truthfully 50-60 mi/wk is sufficient. If I don't eat too many desserts.
Last Feb. the hybrid was stolen. I bought a Trek 3700 MTB. The police recovered my hybrid in Mar. So now I have 2 bikes. Usually commute on the MTB. But it's nice to have a spare when 1 is in the shop.