This option is very much needed.
From what I understand, Alfred makes it possible to set ⇥ as an alternative key to show the Action panel -- which seems quite natural for users coming from Quicksilver. But since there is no way to use an alternative key for autocompletion, this creates a conflict: using ⇥ to show the Action panel makes it impossible to use autocompletion.
Note that this conflict could be avoided without even having to set an alternative autocomplete key, by simply considering multiple ⇥. The first ⇥ could be reserved for autocompletion; but once autocompletion is done, the second ⇥ could bring up the Action panel.