If you have a beer of a specific carbonation level you will be required to dispence that beer (if using CO2 to dispence) at a very specific pressure.  So you do not have the ability to increase or decrease pressure to change the flow speed out of the tap.  For this reason you need to either adjust the beer line length, internal diameter or use flow control devices like this to ensure your beer comes out the tap at the right speed.  Ideally between 250-400ml/10 seconds (based on the standard 10mm ID spout)

Flow control devices are good but they inherently can create a small amount of turbulence and therefore can cause foaming.  In the past flow control taps have been the only common option.  Flow control taps like these ones are popular however they have the issue that due to the fact they are placed right at the end of the beer line they have no head pressure.  As a result any turbulence created can cause foaming and carbonation to come out of solution.

Flow control ball lock disconnects like these on the other hand have the ability to restrict the flow before the beer enters the beer line so the head pressure created by the beer line keeps the carbonation in solution.  Even in the instance that high turbulence is created the beer will be far more resistant to foaming issues.  For this reason flow control ball lock disconnects like these have significantly better performance allowing you the flexibility to adjust line resistance easily but without the introduction of turbulance that creates foaming.