Agree with the above answers. We'll not use Cheers in formal letters or office emails.
Eg If the addressee is a Corporate - Dear Sirs, end with Yours faithfully
If the addressee is a person Dear Mr/Miss Chan, end with Yours sincerely.
In office emails, end with regards, kind regards etc.
You will end a letter/email with Cheers if it is an informal/friendly type of letter/emails - no particular meaning, it's like saying Bye but you wish to end the mail with a happy tone/note.