On one hand, preseason friendlies definitely do not matter. On the other hand, preseason friendlies between teams like Chelsea and Bayern Munich definitely matter.
Not for any competitive reason, of course. When Bayern and Chelsea met in the International Champions Cup Tuesday, Munich's 3-2 win wasn't predictive of anything. No, the Chelsea-Bayern friendly definitely mattered because we hadn't seen elite soccer in a while and missed players doing things like what Thomas Muller did.