I once had thousands of dollars invested in a vocal booth and a drum booth at my original studio. I even had a guitar amp chamber that you could lower a guitar amp into, and if you really wanted isolation, you could put the guitar amp box inside of the vocal booth. I remember recording a Vox AC30 inside of the control room!
This isolation came at a cost. My recordings suffered. I could not figure out why either…the answer was right in front of me!
Sound happens in rooms, not vacuums. I never knew the importance of lettings sounds be out in the open, and letting them breath. The vocal booth (and other iso booths) were killing my recordings, and I never knew it until years later.
…This is why I never use a vocal booth.