This acquired a reputation for being a fun thing to browse, back in the days before the Web. Nowadays it isn't useful. If you want to look something up, the internet is much better. If you want to browse, it's much more fun to browse Wikipedia or TVtropes.
Also, this book is out of copyright now, so you can get free copies online.
I remember being unable to put down an earlier edition of "Brewer" (unfortunately, I can't say which one, since I don't have a copy). What it had that the current edition has much less of was an exhaustive collection of allusions to classical literature and mythology. This made it indispensable if you were reading 19th Century literature (or earlier), where allusions to these texts were not only more common, but went unexplained because contemporaneous readers didn't need the explanation. The current edition has cut much of this - admittedly obscure - material, presumably to make room for items of more contemporary appeal. "Brewer" was at least as much fun to "dip into" with nothing in particular to track down as it was for reference use. I suppose "sic transit gloria mundi" in this context is blasphemous, but that's how it feels...
I've had my copy for at least 20 years. A few times a year I pass by, pick it up, and am fascinated by the great articles about interesting artifacts of speech and culture.
every time I try to look something up in it, I am absolutely guaranteed of not finding it. Perhaps this is an effect of searching from general to specific. Before going to Brewer I've usually gone to an unabridged dictionary and encyclopedia and perhaps a specialized dictionary. Only after trying everywhere else do I try Brewer and don't find it there. Can't figure out how to USE it.