For the last 3 days of the game, which is called the home stretch:
The rate of income from your transporters doubles in value, this is important because as Mabruk said you have to log in often to spend it or your safe will be full. This time is when you may try to spend as much money as you can to max out transmitters and get the achievement bonus for expanding your transmitter network.
The rate at which you earn research points doubles. This is important because maxing out the phase 8 tree takes a lot of points and is tough to do even without the bonus 3 days at the end.
The awarded terra-points on every colony doubles. In the home stretch the colony will level many times and often, if you want to move ahead you can gain ranks in the last 3 days by logging in often and updating your routes to the new resource that appearing on the colony.
The time to level up a building decreases, apartments have 100 levels, each time you level the each building you get more terra-points. In the bonus 3 days is where you may be trying to max out the apartments if you have not done so already.
The race rewards double in value, they double in value when new races appear that were not already up when the "home stretch" timer started. (After the current listed races cycle out).
In the last 3 days you will want to make sure you don't end the game with any energy left as this does not transfer to the next round, here it is advisable to use the "Energy Cooling" button that consumes energy and boosts the speed of your transporters for 30 minutes.