Usually the differences are down to some zeroing out chances that are flagged offside but the play never stopping because nothing came of it. And besides - its very evidently not pointless. Even if there are discrepancies between sources it still gives a lot of information. Information is good. Team analysts use underlying stats like xG (whatever reliable source they use, likely something like statsbomb) to help analyze their teams. Hell even managers like Tuchel openly talk about it in press conferences. It's just a stat that strips away the bias of "shots" and goals and focuses on the quality of those chances. Because creating systems that create more good chances and preventing them is repeatable over time, while scoring low % chances is not a repeatable thing.
Public xG stats are just used to help the public analyze who is truly good and who is lucky (so far). Does it matter? I mean, nothing matters for the public because at the end of the day they are using every single stat to just talk to somebody else and say "so and so is shit" or "so and so is good". So no, it doesn't matter for the majority. It matters a hell of a lot for actual clubs, scouts, analysts, etc. But in terms of general discussion, of course they are still useful. The little discrepancies in individual games get pretty flattened out over time anyway. XG has always been a tool best used for long term analysis, while it's usable for single game analysis just on a basis of seeing how the chances were distributed. Palace being at 0.56 or 1.04 doesn't matter that much, round to the nearest whole number and that's still ~1 goal they could've scored (that huge chance off a corner, and then likely that Benteke chance that wasn't zeroed out). They still had a huge opportunity off a set piece that we were lucky to get away with, and let us go on to get the win basically.
