From a defensive point of view the problem with combination attack or what is called continuous attack in Krav Maga is that if you do not execute defense combined with immediate simultaneous counter attack, you are just moving yourself to another position.
Your opponent now is closer and can reach you and will use the time you take to block to continue attacking you. So if you blocked the first strike or kick, your hand or leg or body moved to one direction you are still subjecting other area of your body to a follow up strike.
Since the opponent is now closer, your brain will not have time to process the second attack since the opponent is right in your face, and the split second he decides to hit you again from any direction will follow up with a hit.
So you cannot afford just to block, or move backward or to the side. Perhaps forward with a counter attack, take-down as last resort grabbing a soft pressure point in the head area or groin area, or using the head itself to apply leverage on the cervical spine...
From an attack point of view, you
want to move in and chase the opponent until you control him if possible or until there is no need to control him. However, to avoid the possibility of getting blocked and counter attacked you need to make your moves unpredictable.
If you are choosing an unpredictable combination you are taking a chance, assuming an area that your opponent might be under trained and unaccustomed to respond to .
If you tailor a combination as needed, you are responding to the opponent counter reaction. But hypothetically let's assume your opponent is well versed in all the principles and applications you are versed in.
Well if you maximized your training based on predicting capabilities based on the opponent’s position before he enters your personal space and not waiting to see a clear punch or a kick or a blade under the constraint of reaction time, you have a very good chance to start with.
Remember that the process from start to finish only takes few split seconds and each one is very critical. Remember to hone your basic strikes and kicks so you would not lose the first chance you get to neutralize your opponent because it might well be your first and last critical chance.
Now imagine yourself knowing all the details of what drives your methods of training while imagining your opponent as trusting his coach which is versed in hard generic training of a fighting art. Information and training methods get lost, forgotten, missed etc.
You are the final control of the process. You need to back up your confidence with the chain of events of your learning process.