Steps followed :
1) A user is booking a room (from their browser), he selects a room that is suject to approval
2) That trigger a mail that is sent to the person in charge of the approval
3) In that mail there is a link, that the approver opens (via the browser)
4) that opens a form to accept or reject but the button are not present if the browser has no Java installed
For one customer java was not permitted to be installed and so they could not approve these requests.