Dislikedleave him alone man. he's a joke and it starts to show. granted he wrapped his BS in a lot of techno talk. made it hard for newbs.Ignored
All markets have their distinctive "rolls": the amount that they will oscillate when there is nothing forcing a higher rate of arrival of 'outside' buys or sells. It's caused by consistent risk management/profit max'ing behavior of the market makers, whether it's specialists on an equity exchange, the 'locals' in a futures or options pit, or the dealer banks in forex.
Cloggie identifies the roll unit of the E/U as 20 pips. Someone could put volatility measures or order stats or some other formal methodology to work and find that themselves, sure: but only if they got the idea to measure it.
So when someone suggests it's an important micro-structure element, and identifies the typical size, that's valuable for new and seasoned traders alike.