So, it seems we're all finding it difficult to concentrate on reading large amounts of text, and getting more easily distracted from....oh, shiny thing!
Ahem...yes, so...I suppose the techniques frowned upon by the Oxford History professor in the article may well be naughty to use when trying to study and analyse literature....but in legal research, they're a godsend! Databases may well throw up hundreds or thousands of hits when you search for a specific term. Once you've narrowed it down a bit more, you're still left with dozens of articles and cases to wade through. And nobody's ever claimed that legal language was snappy, or easy to skim.
The ability to go into these items and search for a specific word is great: by being able to find words instantly, and get some understanding of their use in the case or article through looking at the context, discarding irrelevant items is a much faster process.
I'm not a lawyer: I don't necessarily always understand exactly what it is I'm being asked to find, and despite being a naturally fast reader, I can't dedicate hours and hours of time to fully go through each article or case that may possibly be relevant to get to that level of understanding. Looking for key words helps me narrow down the material, meaning the lawyer gets what they need, faster.
So yes, slow reading's a good thing, in the right situation, but reading legalese is already slow enough - I'm taking all the help I can get with that!