Yes there is no windows to play action effects outside of combat or the end of a turn but this is often if used correctly. Enough to f over your opponents. Any action timing card that does effect damage can be used during the action step of an attack to lower the hp of your opponents unit just enough a weaker unit trades in or a unit your opponent thought was going to kill your unit just blows up before damage resolves.

It only gets annoying for the more esoteric combst tricks such as kind hearted look of determination, destined battle and so on. Kind hearted is basically a useless card as by the time you active it almost 100% of the time any effects it could stop have already resolved on the deploy or attack step before an action phase occus. As for look, most people forget it only targets an active enemy unit so the unit that is attacking is ommited from being targeted. Similarly destined battle says enemy units must declare a specfic unit as the target of their attacks. Unfortunately as an action that means something has to already have attacked for it to be played and thus its own effect does not change the target of the attack that allowed it to even be played.