Everyone must consider the pros and cons of different charging and storage options as they relate to their own particular needs and situation. For some, simply storing energy in batteries is plenty. If you drive every day, long enough for your alternator to fully charge your storage battery system, and your needs are small, great! If you like to find a lovely spot in the wilderness and stay for days or weeks, you will need some alternative means of getting energy into your batteries, whether by means of a generator or, if you want to be more free of fossil fuels with their noise, smell, expense, etc, solar is a good option.
I've been using solar energy for 4 years. I changed rigs a few months ago, and the new one has a great big ol' generator, so I thought I would be fine. Four months into that, and I just had 900 watts of solar installed! Ahhhh, freedom from noise, stench, vibration, and the constant need to replenish fuel!
Hope this helps.
The Dire Wolfess