Well integrated subs are a must for any serious system. Without them, if your speakers can't do 20Hz flat, you are missing what's on the recording and what the musicians/recording engineers intended for you to hear, period.
I wasn't a very big fan of subs, I've heard some setups that were impressive REL Stentor III and Studio III but thought I could live without the $10k sub... Still, I've always wanted to see what a pair of well designed subs can bring to the table in my own system. When the JL Fathoms came out and started getting all those stellar reviews, I decided to pull the trigger and give them a try. The "tweakophile" in me also wanted to experiment with a high quality crossover, so the Bryston 10B was selected for the project. All I can say is that I can never go back to listening without subs again.
I will agree on one thing though, if the subs can't be integrated in a way that they become sonically invisible and simply a smooth extension of your speaker, I would rather live without them. The artificial bloat and bass heaviness and overhang would drive me crazy. The Fathoms are anything but that, they are the most musical subs I have ever heard.
Right now I am listening to Hugh Masekela "Hope" album and let me tell you, this recording has tremendous dynamic range and very well recorded drums, without the subs, I would be missing much of the "musical impact".