Some say that dist-upgrade is to upgrade the distribution... Actually, that's not true... Its an old story...

The man pages say that 'upgrade' will update the packages without touching the dependencies and 'dist-upgrade' will also touch the dependencies and remove them if it wants to.

I can't fully understand this... Can some one please make this clear? A full explanation? Is it a risk to use dist-upgrade? Why do we have two commands like this?

Thanks in advance...