Thor159 :
Why 25 is needed can you please explain.
I am little confused.
Is not needed, is recommended.
You can run Ubuntu properly with just 10GB, but that's about it. No much more apps or programs can be installed, therefore i recommend that you put a little more space into it if you're going to install some more things in it.
Linux is a very open-minded OS and you can do pretty much anything you want with it.
If you're low in space or PC-Specs, you may use Lubuntu or Puppy Linux which uses less resources from the PC as well, therefore can be installed with less memory available also.