It all depends on the numbers.. If all you ever gonna get is one shot, or your whole army relies on pinpoint accuracy, then it is not that much..
But say, orks, that naturally hit only with 5+, its gonna be a huge boost to them imo, since its basically already incorporated into their stats (or weapon stats that is).
Also, Squad of lootas would be hitting on 5+ if they were stationary, now they can move and hit on 6'es, theres really not that much difference to say a Marine will be hitting normally on a 3+ and now he would need 6 to hit..
Also, theres a lot of difference if you charge on 5 man tactical squad (or even 10man). They will be rapid firing you for 9 shots if sergeant has pistol (19 if its 10man squad). Now, normally its 'balanced' so that these guys will need 3+ to hit on a str4 weapon. now its 6'es.
Compared to a 10man loota squad that normally hit on 5+. Now you charge and they overwatch shoot you: up to 30 str7 shots that hit you on a 6+..
See the difference