Like the impersonal phrase "loved ones" that derived from funeral homes where obituaries are constructed, the parting phrase "Thanks in advance" or, more simply, "Thanks!" is a poor choice for what the writer needs to use in a piece of workplace communication because it sounds like where it came from: bill collectors.
"Madame, you owe us money. Send it today. Thanks in advance."
That's the general thrust of a bill collector's message.
Somehow, just as the phrase "loved ones" has seeped into popular discourse to refer inadequately to people in your life that you hold dear, the parting phrase "Thanks in advance" is often the close for all kinds of messages, some of them requests, some demands, and others that require something authentic to the situation, such as: Sincerely, yours truly, best regards. For those are closings to missives, and "Thanks in advance" is not.
It's a matter of logic if not courtesy.
If you are making a request, you truly are not making one if your expectation is so high as to thank the person in advance for complying.
And if the person has not yet complied, gratitude is out of place.
More often, that closing feels presumptuous to a reader.
But perhaps you don't know that.
The next time you refer to your boyfriend, girlfriend, husband or wife as "loved one", stop and muse whether he/she likes the inadequacy of the sentiment.
Then, reconsider ever using "Thanks in advance", unless you are, of course, a bill collector just doing your job.