It gets even worse. I was doing some web dev in the last couple months and I noticed that my "localhost" was ridiculously slow. At first, I thought it was NPM/Gulp but then I noticed that it behaved irrationally, sometimes it is slow and sometimes it works.
The problem was: Parental Control. Apparently, every request was checked and thus slowed the whole thing down. Needless to say, a couple days at least were wasted in this.