It's quite simple really, it's just another football metric for data analysis of player performances.
Like all metrics, nuance and relative comparisons to other metrics and other players are required, as well as a long time frame to make inferences upon them.
Those against these types of analysis are simply going to be left behind in terms of where football discourse is going, and has been going for the last 5 or so years.
It also contextualizes more abstract things like "he is a bad finisher", or "he is a bad creator".
This doesn't apply to just xG but to all these new metrics, numbers are not inherently bad, its how you interpret them, and football has been far behind other sports in terms of this ability to analyze and interpret player performances.
xG
In particular to xG, it also requires nuance, for example, 2 teams can rack up an xG of 2.5 in a game, but maybe one team did it through 25 shots, and the other team through 10, that is useful to then infer, the team with 10 probably had higher quality chances, whereas the other team was making more speculative efforts, that increased the xG stat, most would much prefer the scenario of the team with 10 shots.
For players, its useful over a long time frame, to see how good their xG compares to their actual goals, it leads to certain conclusions that can also backup the eye test such as "Darwin Nunes is a shit finisher, or the xG to G numbers clearly show this", you can even see stats that break down xG/shot to see if players are just getting alot of shit chances, or lower but higher quality chances, its useful.
xA and SCA
I like these 2 for chance creation, xA doesn't need to be compared to assists, unlike xG, because its irrelevant whether the player you passed to scored the chance, that's not something the passing player can control.
SCA is simply how many times a game you make your team shoot (make some chance), I really like this one as well because some players don't rank super high on xA but rank high on SCA (David Silva is one who was the king at this).
Be careful with SCA though, as some players who take the set pieces for a team will artifically be higher on this, luckily this stat can be broken down to "live ball" for a more accurate comparison.