Or if you happen to live in a very quiet neighborhood and you and your punk rock band are making your first album, you'll need wall soundproofing in order to keep internal noise from leaking out of your recording room.
In any case, the true concept of soundproofing walls (or soundproofing in general) is somewhat misunderstood by most musicians and home recordists. The lines between "acoustic treatments" and actual "soundproofing" can indeed be a little confusing, given the vast range of studio setups, multi-purpose rooms, and even the actual construction of studio walls. Soundproofing a recording studio does infact leave a number of options quite wide open, so it's best to narrow down through process of elimination exactly what it is you want, and what it is you'll actually need.
Hopefully, you didn't hear much of anything. Low decibal noise coming from outside your house or apartment won't bleed into your recordings that much unless you're doing mostly acoustic work.
But if there's a steady flow of traffic and street noise near you on a frequent basis, or any kind of constant leakage of audible sound into your recording room(s), you'll most likely have to devote some time and resources to soundproofing walls.
If however you happen to have windows in your recording room, it's possible that a major portion of your problems can be solved just through some simple window soundproofing techniques. (Skip the following article obviously if you don't have any windows in your recording area.)