Well when I first heard about this tax, I freaked out to be honest. I did not understand it's purpose, and I don't understand fully not even know. However, I can say this. My view is that it will not change much, nonetheless it is one small step towards making this game better.
This tax solve some problems a lot of you guys are not even aware of. In bigger countries you had to lose money in order to win the championship. Now the tax gives you the incentive to train more and overspend less. Champinoship runs have turned into who can spend more, preceded by season or two of saving, making it basically a mini B3.
Look at my league. Maybe I'm an exception because I was tanking last season, but I'm not the only one with 600k+ roster - there are two others with such huge salaries for D.II. One of them is not training much, so his training exemption is probably very small and he has to pay overextension tax. When he figures out he bought too many salaries at once, he will probably sell some of those players in order to avoid losing money.
So you can afford to spend a lot in order to win championship only if your training exemption is big enough. Which means making your team better only with transfer list help isn't an option anymore. Remember we voiced our displeasure several times about how a well-trained player at 26 years costs the same as a 18y old draftee? Well that won't be the case anymore. Less teams will be able to afford those 26y olds and will rather spend a bit more time training, which will balance things out a bit.