On Sep 30, 2015 9:56 PM, "Mike Hearn via bitcoin-dev" <bitcoin-dev@lists.linuxfoundation.org> wrote:
>
> Jorge has said soft forks always lead to network convergence. No, they don't. You get constant mini divergences until everyone has upgraded, as opposed to a single divergence with a hard fork (until everyone has upgraded). The quantity of invalid blocks mined, on the other hand, is identical in both types.

Exactly, all those "mini divergences" eventually disappear (because we're assuming the hashrate majority has upgraded and non-upgraded miners accept upgraded blocks as valid), even if the hashrate minority never upgrades.
On the other hand, the "single divergence" in the hardfork keeps growing forever (unless all miners evetually upgrade.
With softforks, we maintain eventual consistency, with hardforks we don't.