Intent of Offer Vs Offer

Good Morning
I can share my previous company experience. I was working for multinational retial chain based in Middle East they were having this practice of issuing letter of intent to candidates after the interview for the local as well as overseas candidates. Once the candidates visa processing and all other formalities were over and the candidates landed at the respective country to join after joining they used to give him offer letter which candidates signed and one copy goes to candidates personal file. I think this is an international practice just to keep the selected candidates on hold or they can keep the candidates reserve for them so that candidate will not look for anyother job oppertunities. If everything goes well then candidates will join the organization or else they can say to the candidates that we are sorry we do not have opening.