I'm a little guy in terms of stature, so let me say something.
If you mean 'Little' in terms of Strength, then less strength + same technique will result in an obvious winner.
If by 'Little' you mean same strength, but lighter, then you have an advantage. The other guy will have less cardio, and although the strikes are stronger, they will not be able to pull the arm back as fast. This allows for easy manipulation of the arm for Locks/Throws, or a counter like an Uppercut or Overhand.
If you mean 'Little' in terms of stature alone, then taller guys have:
Longer Strike Recovery, more distance to return to base.
Less Coordination, as longer limbs mean they are further from the body and therefore often leads to less accuracy, but this is not always true.
Less Endurance. You have to move further in order to strike, therefore more energy is used.
Less Speed. Shorter guys muscles aren't stretched out as much, so they can contract quicker and therefore move quicker.
Less Agility. Not really sure why, that's just the way it is and the way most people will seem to find it.
Less Balance. Lower Center of Gravity means better balance. Simple as that.
Taller guys have: Reach, More power in some strikes when striking down with gravity, High Center of gravity can lead to weighing down, POSSIBLY more weight as they have more height (Although this can also be seen as a disadvantage)
And that's only in boxing, but it applys to other things as well. At school the other day, my friend said 'Stop picking on the smaller guy' in relation to me as I asked another friend to show a Jujutsu move we learnt. I'm not the weakest guy in the world by any means, so I assume he was joking. Anyway, I told him that it made no difference about anything, if I tried to get up I would break my wrist. If anyone tried to get up, anyone would break their wrist. If he wanted to, he could have broken the shoulder and the wrist of anybody.
