For example: France offers specific saving deposits with guaranteed interest rate and non-taxed. If a normal saving deposit would be taxed and has similar interest rate, "optimizing their tax" means just using the that specific deposit.
There are many other schemes that I can't believe they exist (example: in France if you create an investment account, after 5 years of the account existence you are not taxed on the gains! So what you can do is "create account with 100 euro", "wait 5 years", "invest more / potentially do gains" - and you will not be taxed!!!)
You will tell me "that is morally wrong!". I could agree with you, but I see nobody demanding better laws/regulations, probably because they don't know/care about details.
No, I think the investment account with no tax on gains is fine. I'm talking about things like "create a company, take a salary that's just over the lowest tax threshold, get 0% infinite term company loans from yourself" - things that your average person wouldn't be doing (unlike the free-gains-account.)