there are two variables to carbonating beer (temperature and pressure)
there are three variables to balancing your system (temperature, pressure, and line legnth)
if your line legnth is not adjustable, then you can adjust your temperature and pressure to match it (but obviously you can only adjust temperature so far before you are drinking warm beer or sucking on a beer ice cube). having a certain line legnth means you will have a certain pressure that will give you the best pour. you can then look on a carbonation chart to determine what temperature your kegs should be, at that pressure, to get the desired carbonation level.
if your lines are too short, you wont be able to set the pressure high enough to maintain the proper carbonation level because the beer would be exploding out of the tap (so you would have to decrease temperature to make up for that, but you can only go downto 32 degrees). also if your lines are too long, you will need to use a lot of pressure to push the beer thru them, and have to increase the temperature of the kegs to match that pressure, to prevent over-carbonation. if your lines are wayyyy too long, the temperature required will be too high to enjoy the beer at.