And I don't fully agree with
@Reyesnuthugr when he says the jab cannot be powerful. I believe a counter jab to a jab, or a loaded jab after a 2, can make enough damage to not be considered light sparring...
Just to clear this up^^ I didn't say a jab can't be powerful (they can occasionally KO someone but it's not overly common) , but you can't really complain about someone throwing jabs "too hard" in sparring because the power is limited compared to the other punches (which is why it isn't counted as a power punch in boxing scoring) due to its design/mechanics.
If someone's jabs are "too hard" for you in sparring, then sparring isn't for you. They can be stiff, they can be unpleasant, they can even bust your lip, nose or the skin over your eye sometimes. But they are by far the weakest punch in boxing.
The only likely scenario where jabs are "too hard" during sparring is if someone is really pouring them onto a complete beginner- but then it's not the individual power of the punches but the overall intensity. Either that or maybe if you outweigh your sparring partner by 80 lbs and are going HAM, then I can see it
maybe. In a case like that where one of the sparring partners is terribly outmatched, using only jabs is a common way for gyms to greatly limit, and basically prevent damage.
Hitting someone too hard with jabs is basically something that is so difficult to do you'd have to be deliberately trying your best to do just that (and also be mismatched against your sparring partner by quite a bit), which is why I recommended them.
---
Also, if you're throwing mostly or all jabs during sparring, it will help you become very sharp at boxing in general (it's like a useful limiting drill) and make it so you can't rely on power but are forced to use all the other fundamental tools you are
supposed to be using-- angles, timing, etc.
It's basically the opposite of cheating. Handicapping yourself (a little- the jab is incredibly versatile) to learn on a quicker curve.
If you get good at jabbing, you can always EASILY add other types of punches in later with what you have learned and they will work all the better with your new appreciation for distance, timing, movement, angles, etc.