Proofing requires more dead air in between walls as to not let the vibrations of the sounds travel. There for unless you have a room planned to be built inside of an existing room its better to just try and reduce (deaden) the sound then to try and take the sound (proof) out all together.
There’s many different variables to look at when trying to reduce reverberation. One of which would be the most important is: How loud do you plan to be in said room?
My opinion may be a bit biased since I’m looking at this as recording music or as a band practice room. Recording studios are built with many different variables in mind. No central air (mics can pick up the hum sometimes), separate rooms for each instrument, not to mention the recording area is probably surrounded by dead air (e.g. rooms inside of rooms). So, having tried to explain some of this, I doubt you’ll be needing to go to this extreme, but I feel the difference between Proofing & Deadening is quite clear.
Here’s a good rule of thumb. Bass is the loudest frequency. Loudest as in it travels the furthest by vibrating through things. Things like carpet and foam can reduce the traveling of the frequency, but things like walls (which are virtually solid) easily let the vibrations passed it. So, this brings us back to question, how loud do you plan to be?