Answer:
a. Groupon presented the Adjusted Consolidated Segment Operating Income (ACSOI) because it shows a higher amount than EBITDA. The reason is simple, Groupon wanted to show higher revenues and earnings, and the way they thought that they could do it was to use what I call "creative accounting". If the numbers do not match your expectations, play with them and change them until they do. That is exactly what Groupon did.
ACSOI increases EBITDA (which is a non-GAAP metric but it is accepted as valid by all companies) because it excludes certain expenses, e.g. marketing expenses, stock compensations, etc. It is irrational to believe that marketing expenses in a company like Groupon were irrelevant. Just a few years ago Groupon was the fastest-growing internet services company, and online marketing was essential for that type of growth rate.
b. We can just compare EBITDA and ACSOI, both are non-GAAP metrics, but one is properly designed, useful and actually shows how a company's cost structure works. But ACSOI is deliberately used to fool investors.
Some non-GAAP metrics are very useful, such as managerial accounting. Financial reports are tools and how helpful or useful they are depends on people. If you try to fool investors and trick them, eventually they will realize it.