I am also curious about the benefits of this.
I am an EUI citizen, my wife is entitled to a British passport through her father, and my kids are entitled because theyw ere born here.
I want a British passport, and have no concrete reason why, except "because I am entitled to one", and because I see myself and my family living here for the next 20 years or more.
I suspect it may become more difficult to get one in a few years, and want to get it while it is relatively easy (if a bit expensive)
If I wanted to move to a Commonwealth country, would the British passport confer any more benefits than another EU passport?