How many images generated by Customizr?

There are a lot of thumbnails, you can certainly remove the automatic creation of the thumbnails, but it depends on what you use.
For example:
if you use all boxed slider you can avoid the creation of the full-width slider images,
If you don’t use the grid layout anywhere in your site, and you don’t plan to use it, then you can remove the grid thumbnails.. and so on.

Each thumbnail (image size) is required by a certain goal.

In my case (freelysoft.it), I can remove such images? And how can I prevent their creation?

in your child-theme functions.php something like:

add_action('after_setup_theme', 'remove_some_img_sizes', 9999);
function remove_some_img_sizes(){
  remove_image_size('slider-full'); /* prevents slider full creation */
  remove_image_size('slider'); /* prevents slider boxed creation*/
  remove_image_size('tc-grid-full'); /* used for the expanded featured in the grid */
  remove_image_size('tc-thumb'); /* used for the alternate thumbnail and the post thumbnail in post pages*/
}

hope this helps.