As it has been explained many times, it was a bug, not a feature.
When you modified tags in 0.8, changes were always written to foobar2000's database even if the files had not been updated successfully, for example due to "Block tag updates" being enabled, or the files being read-only. Some people misleadingly perceived this as a "database tags" feature.
Edit: Found a post by Peter about why he is not going to add an option to block tag updates:
QUOTE(Peter @ Mar 1 2006, 00:08)

Adding a tag update block option won't prevent malicious / badly written components from altering your files anyway, at least as long as all components are native code and not sandboxed inside a .NET virtual machine or something like that (which won't happen anytime soon for multiple reasons).
Adding a special switch to keep users from shooting themselves in the foot is a step backwards; people's components should be designed in a way that makes it obvious at which point tag updates take place, and give an option to cancel the operation before any harm is done.