I use a mod called XVM in World of Tanks. It calculates a score called WN8 for each of my battles, and gives an aggregate score of my and the players I meet in battles (if they don't want that, they can use the anonymizer). The WN8 score has its limitations, like not counting assisted damage at all, and over-emphasizing damage over other contributions to the battle. But I still find it useful as a learning tool to improve my game. However, I don't obsess about it, like some people do.

In every game there are people who use the available scores as a source of self-worth. "Look at me, I am a better human being, because I have a higher score!". So a WN8 score is extremely important to some people, which is not always a good thing. Besides leading people into actually playing worse, more selfishly, and lowering the chance of their team to win, the most obvious thing is stat padding: If you play a lot, your WN8 improves; but that can take thousands of games, and your statistics are forever weighed down by the low scores you had at the start. And the further you advance along the tiers, the harder the battles become, which also tends to lower your score. So there are quite a lot of people who make a new account, and then systematically only ever play in low tiers. They have thousands of games on low tier tanks. That makes their stats look good until you look at the details. But it is bad for the game, because they are basically preying on new players, which makes World of Tanks a less good experience for new players than it could be.

So some people argue that it would be better if XVM and WN8 or similar scores were removed. While that is unlikely to happen, at the very least today patch 1.9 will kick off another discussion about stats: Patch 1.9 massively changes a lot of tanks, especially at lower tiers. They will get more hit points, thus survive longer, more ammo to be able to fire for longer. A lot of tanks will also be rebalanced, and the tech trees will be revamped. And all these changes will mess up the statistics. WN8 calculates you score by comparing your performance with an "expected value" for your tank. And these expected values will change dramatically, especially a low tiers. But the databases that XVM use don't hold individual values of each battle, just averages. If you drove in a tank before and after the patch, XVM can't know how many of those battles were before the patch and how many were afterwards. XVM just sees the average, and compares that to a new expected value, which I assume will be recalculated upwards.

In short, the more battles you did before the patch, the worse you will look in the statistics. Even the stat padders who spent countless hours to achieve a high looking score on XVM by driving low tier tanks will suddenly not look all that good anymore. If you want better looking stats, you will have to reroll again and start over. At the very least there will be some heated discussion with veteran players complaining that their 10 years of playing World of Tanks are now dragging down their statistics, because post-patch values will be much higher. Some people will certainly shout for Wargaming to reset all statistics in the database that XVM uses.

For me that will be interesting to watch, but I don't feel very affected. I don't care what my average WN8 stat is saying, I am more interested in stats for individual battles or sessions, and whether I am getting better or not. I simply won't compare my new stats with the old ones, and disregard the now somewhat irrelevant average. But I am interested in seeing whether this will lead to changes of the XVM mod.