I guess the hope is that the servers and stateroom hosts will somehow provide even better service if they receive a partial tip up front. However, I really doubt there's much advantage in partial pre-tipping. It's certainly not the way it's usually done. It just seems like extra trouble for the passenger and for the service staff.
I think most servers and stateroom hosts will provide outstanding service because that's what they do -- and a "down payment" tip up front won't make that service any better or worse.
It could even backfire if one the people you're tipping doesn't understand the term "down payment" and simply thinks he or she received their entire (possibly substandard) tip up front. For most of the staff, English is a second language. And while we had good experience with the staff's language skills, an English language business term like "down payment" may not have meaning to some percentage of the service staff members.
Be nice to the service staff, so that they enjoy taking care you.