Actually I'm afraid the bit of that advice concerning disabling is partially incorrect, though the bit about moving media to removable storage is good.
You can only disable pre-installed apps, i.e. the ones you can't uninstall. When you do this it does 3 things: it prevents the app running (and removes it from the drawer), it erases all data the app has stored (which does save you space), and it removes any updates to that app (which also saves you space). Since the original pre-installed copy of the app lives in the /system partition, which is inaccessible to you, removing it from there would not free up any more space for you. Hence disabling is, in practice, as good as uninstalling.
Of course if the app has never been run, has never stored any data, and has had no updates you won't save much space that way - but you wouldn't save any more by uninstalling it either. But if it's been updated it could save you 10s or 100s of MB of space even if you have never used it just by removing those updates.
As for what can be disabled, the system can prevent you from disabling an app, and if the app is genuinely important it will do so. Unfortunately some manufacturers or carriers also prevent you from disabling stuff that is irrelevant crap, presumably because someone has paid them to stop you doing so. You'd need to root to do anything about that. But the bottom line of this is that if you can disable it, it's probably safe to do so (worst case it may break some function, e.g. if some other system app is hard-coded to use the one you disabled for something - which would be crap coding, but occasionally happens - but it won't stop you using the phone and won't stop you re-enabling the app if disabling it does cause problems).