So for the ignorant, what does thinning do other than the obvious? Allow you to better control coats of paint to get the look you want? I ask because I'm offender #1 when it comes to that video. Probably why I ditched plastic a long time ago.
Without thinning the paints, the detail can get lost and probably the best way to describe it would be it looks like there is a thick coat of colour over the plastic rather than it looking like the plastic is coloured itself, if that makes sense.
I'd recomend reading one of the articles on Google / Youtube videos about it which can explain in more detail. But in short you'll see your painting improve greatly.