So whilst a CMS does has it benefits, they're some that are a nightmare.
@Arunjit: I agree with you there. But I'm yet to come across the CMS that produces clean codes. Most of the ones I've used (and I've used quite a few) end of giving more problems than solving them.
It's easier to start developing your site with a CMS but nothing stops you from integrating same into your site later on provided you know what you're doing.