For me it solves a real issue, a lot of the code that I work on looks like this: (defn foo [{:keys [a b c] :or {a 1}] {:pre [(some? b) (some? c]} ..

For me it solves a real issue, a lot of the code that I work on looks like this: (defn foo [{:keys [a b c] :or {a 1}] {:pre [(some? b) (some? c]} ..... having `:keys!` will automatically remove the need for `:pre`