Support only segment-based URLs

As far as I know there are no real draw backs against only segment-based URLs.
The advantages:
- More search engine friendly (although you can read in a lot of places this is not a valid argument anymore)
- Easier for end users to understand / more logical and meaningful
- It's prettier (Am I really saying this?)

Is there more? Is there any reason not to have segment-based URLs only?

But is the idea to have the Codeigniter framework handle this entirely, or is it okay to still work with a .htaccess file?