Combo refers to the number of consecutive notes a player taps on and gets a 'Perfect' or 'Good' rating for the note successfully.
Combos can potentially affect a player's score for a song depending on the accumulated combo.
For example, a player can get a miss on a song right at the start of the song. Another player gets 1 miss too, but misses it in the middle of the song.
Formulas for calculating Score and TP:
As when you refer to the formula for score, you can also find out that the former got a higher score on the song as compared to the latter, for the same song.
Thus, accumulating a high combo is essential to get a good score no matter how many notes you Missed. The same applies towards TP calculation, except with Black Perfect and Colored Perfect