A few years back I cycled for maximum gain/maximum weight loss. I spent the rest of the day 6 days a week with low energy, but I did loose 10kg in 3 months. Then I injured my leg in an unrelated accident and was unable to cycle for several months. The weight just came back. This year I'm just cycling 20-30km every moring at a pace that doesn't leave me too tired. When it gets too easy I try and move the average speed up a few points until it starts to hurt just a little. So far its worked great. Taking baby steps and cycling before breakfast I've noticed a real improvement in my ability to cycle, and it leaves me with much more energy through the day.
On a Saturday or Sunday I'll push for 50-60km or until I feel like I'm going to die, but its not a good idea to do that too often or you lose the motivation to get up at 5am and ride.