I would say it depends on the equipment. I used to use a Brevillle Barista Express that did a 10 second pre-infusion by default. As I learned the machine I found I could get better results without the pre-infusion. I am currently using a Gaggia Classic Pro which does not have a pre-infusion function, but some people open the steam valve to get a low pressure pre-infusion. I find this technique will lower the temperature during the shot so I do not use it, but could be useful in some situations. I also have a Flair manual machine, and always use about a 10 second pre-infusion before ramping up to full pressure. These are 3 examples of why I don't put any value on "data" or internet reviews, because setups are so different that making a general statement or conclusion may or may not apply to any specific setup.