uh so there's

1. hit combo (the big numbers that appear on either end of the battle field. counts how many times your team lands a hit on their other team without them hitting back/dodging. high hit combo triggers chases like KoH)

2. chase combo (counts how many times u can go repulse-knockdown-lowfloact-repulse-knockdown-lowfloat-repulse-etc. also contributes to hit combo)

3. combo (the substat)

so which combo are u asking for? XD

then yea, as far as i know, it helps to trigger 'high combo' chases like koh, crab, gerotora. it helps u land additional attacks on units with super armour, and also provides a way to use aoe chases (ninjas not affected in the regular chase combo will also suffer damage from high combo chases) which is very useful and helps to deal more damage overall.

some high combo chases also cause immobile (anbu yamato, edo hashirama), and it's always to random units. the unpredictablity of these high combo chases can be very useful in pvp fights.