The plaintiff is arguing that GOOG is guilty of intentional spoliation of evidence, and that execs deliberately moving conversations to ephemeral channels demonstrates mens rea; if the judge agrees, they can instruct the jury (or trier of fact) that any missing evidence should be construed through the lens of “adverse inference” — in other words, assume that the missing evidence is, in fact, prejudicial to the defense’s case. This is … not something you want in a litigation, needless to say.

So, yeah, you can delete evidence that you know could be relevant to any future litigation, it’s just that if a judge finds out about it you’re going to get hit hard over it.