Planners and dispatchers will prevent you from meeting your mileage and hometime goals. There is always some excuse why something happened to put you, the driver, at a disadvantage and then it cannot be undone... making you get home two days later than planned or making you get 300 miles less for the week than you could have. It seems they do not like to see drivers prosper or be happy. They prefer to see you in a bind or failing completely.
Here are their most common tricks: 1. to send you a dispatch over the truck pc that will work out perfect, then cancel it and make you drive something worse or that you indicated is not your preference, 2. send you to a place where you will get stuck or slowed down due to some failure (mechanical, load didn't exist, etc.). It would not be so obvious but you have to wonder if this happens each and every time on your load going home, 3. set appointments so you get home later and later in the day.
Also, if you aren't good at counting your miles for the pay period, dispatchers will have you thinking you got 3,000 miles in the week when you really only got 1600 or so.