The common vibratory pump used in most machines is rated at 15 or 19bar. A regulator is added to lower the pressure to produce 9-10 bar at the group head.
Generally higher pressure means faster flow rate during extraction HOWEVER some experiments conducted have shown if pressure is too high the flow rate will be actually slower because the puck gets compacted so much.
Taste wise is subjective. Many are in agreement that Slow ramp up and preinfusion at low pressure seems to produce the best results.
If you are on a vib pump which naturally starts with a short low ramp followed by a high almost straight line of pressure of say 12 bars.
You'll probably want to use lesser powder with finer grinding.
Maybe where you read are from Americans or Aussies who tend to applying heavy dosages, which will have issues with perforation with higher pressure.
Slow start for pre-infusion, does theoretically provides a cushion to keep the puck better in place while extracting. Maybe a better looking puck, a little more uniform extraction, but doubt it will make it tasting much better.
If the grinder had been tuned correctly and tamped uniformly, with the right dosage.
You don't need pre-infusion. Of course, it's harder to use lesser dose but it does work.
In fact, by coffee science, the pre-infusion prolongs the extraction period which may not be a good thing for the top layer of puck with over exposure of hot water.
But then we can also dispute that by saying the over exposure adds another identify of rougher notes to make your espresso tasting more distinguishable.
Well it's up to the taste buds to decide.
