Most (if not all) pumps have an inbuilt pressure switch, which means that when you nip the hose (or turn the flow off using an aquadapter, or a flow control valve), the pump will realise that enough pressure is built up and it turns the pump off.
When you release the nipped hose, the pressure switch on the pump senses that it can pump, and will pump.
If you don't reconnect the switch, the pump keeps on trying to pump and it blows your joints.
For most pump controllers, you disconnect the pressure switch and the pump controller does the job, so if you remove the flow controller, you need to reconnect the pressure switch.
It's very simple to do and I love the simplicity of it; no pump controller to mess us about. A change of temp used to make me have to recalibrate the thing, and if the leisure battery isn't up to spec, you end up getting messed about and buying a new one too. This doesn't happen with a 'pump only' system. My 'knackered' leisure battery works fine and powers two pumps fine for two days; no problems. Before, with a controller, it worked fine for a morning and then played up.
I like the fast flow rate too; you work quicker - it's physically easier.
I will never work with a flow controller again. They waste our time and money - and they annoy me.
