I think he means they one of the biggest consumers of cluster resources. Each group within google probably has a quota for how many resources they are allowed to use. It's unclear here if their consumption is so huge because they are successful or inefficient though...
Does anybody know what they actually do? I see them mentioned all the time but I don’t get it. Is it just flight information or do they do pricing analysis and other stuff
QPX (ITA's, and now Google's) system is responsible for calculating and searching airfares, i.e. the complete "solution" for "I want to get from A to B with those constraints". It's what responds when you ask google flight for a route, essentially. This is quite computationally complex due to many dimensions involved in airfare calculations. This system is essentially implemented on top of SBCL with some small bits of C++ (responsible, IIRC, for handling memory-mapped airfare data files).
After they acquired ITA, they have few openings in between, and are yet, apparently, one of the biggest consumers of quotas.