It matters because usually only the starting line up is the one that plays major minutes together. No other line-up plays more than 5-6 minutes(I think that was the number, if I am wrong correct me) together a night. You can cherry pick - he played with this guy that amount of minutes and with that guy that amount of minutes, but this doesn't tell you anything, besides "he wasn't always alone on the court, he had a starter most of the time with him". Well, good, but it is much easier to develop when you have stability around you and you play with the same guys -all of them, rather than one or two of them(which is usually the case with subs).