Once you fill the tube with air, the pressure inside the tire (tube) will hold the presta valve closed so that no air leaks out of the valve stem allowing you to tighten the knurled nut without losing pressure. You may lose a very little air when you remove the adapter if you bump the part that you are going to tighten.

Presta valves became popular in the US in the early 1970s when high pressure (100+ psi) clincher tires were introduced for "10 speed bike" owners. Presta valves were used in Europe way before that. The frame mounted pumps available in the 1970s did not work very well on a schraeder valve because you have to add in the pressure it takes to open the spring in the schraeder valve core. So, if you were attempting to get 110 pounds in a high pressure tire, the pump might have to deliver 130 - 140 psi to fill the tire to 110 lbs. Modern pumps are much better at delivering this high a pressure to the tire.

That said, I personally like presta valve tubes better. They are generally lighter than the ones you find in the mass merchandiser bike section. Why spend a lot of money to get a light trike only to add a couple of pounds with those wretched slime filled tubes that they sell at WalMart?