$ date +%z +0100 $ date +%Z CET
Isn't this usefull, I don't need it actually to fall back to Europe/Amsterdam
It unfortunately isn't (for telling if and when the DST shift is), and the Calendar module needs to know that.
If you only use the Calendar module to do very basic operations that time(), localtime(), gmtime() and mktime() could easily do instead, you may want to sacrifice the convenience of the more complex Calendar engine and save some execution time. For cases where you are likely to need better range than the syscalls allow, or do nontrivial time math, Calendar is still probably your best option, though.
(Of course this is not just a matter of execution time tradeoffs; the development time you save on not reinventing needless low-level time treatment bugs by using the library can be substantial.)