Do you know what type & location they do apply soundproof to your car? Soundproof got many materials and different area to paste to reduce certain sound. I seated 1 car with full soundproof, even outside people horn or shout also cannot hear inside.  But the problem, car added weight a lot and feel heavy to move felt like added at least 2 person weight (Est. 100kg++) That car is done in this way due to owner want audio sound quality in his ride and feel isolate inside, so both the soundproof material need to absorb/isolate outside and internal sound (to reduce external, echo & vibration sound).

You need to ask and tell the soundproof person what you want, if not some might go for internal sound proof material for car audio quality setup like 1 member said. If want to reduce certain sound like from engine bay, tire or suspension area, different type of sound proof material need to add on engine bay firewall/bonnet, wheel arch/fender area.

Yes, the owner feedback got few times until got police motorist (VIP escort) knock on his window to tell him move aside..