Live cash, meaning of 1/1/2, 1/3/5 etc

[BeaucoupFish]

Feel like a noob asking this, but what exectly does 1-1-2 mean (or 2-3-5 etc).

Obv two of these figures are for the small and big blinds, but the third is what...the minimum raise?

Also, what is the purpose of this, vs. just 1/2 or whatever.