There is not any advantage to any given multiplier than the amount of money you earn per flight. The Multiplier is calculated on the net of the flight so even if there was no multiplier you would always make a profit if the flight. Having a multiplier on an unprofitable flight will still be unprofitable, just more so.
The best way to think of the multiplier is to think in terms of flights flown. If you have a 1000 multiplier, then every flight flown by you or one of your VA's pilots is the same as having that pilot fly the route 1000 times in terms of how much you make or lose on a flight. The lower the multiplier, the less times that the pilot has "flown" that route.
I use a low number not for ego, but because I don't like to see a big amount in my VA's bank account since I don't want to grow the airline very fast. To me it doesn't make any sense to have a 1000 multiplier when I'm not looking to have 100+ aircraft in my fleet nor am I looking to have a lot of large aircraft. So, having a multi-billion dollar bank account doesn't seem logical to me. As such, I started with much less money than everyone else ($5 million instead of $25 million) and with a 100x multiplier. The VA won't be able to afford new airplanes as often, but then I don't want it to, so it fits my style of operations. Others may want to build that big fleet fast and that's their thing, so they can do it.
As for time acceleration - You get a bonus for flying at less than 8x acceleration and that bonus increases the closer to 1x you get for a maximum of a 20% bonus on your pre-multiplier profits, so there is incentive to minimize the use of time acceleration and people making billions of dollars a day by flying close to a hundred flight hours a day. This was implimented after a couple of users did exactly that and it seems to have done its job for the most part.
