The girdles are a $200 insurance policy. Things like rocker studs do break (often from over-revving). One guy with stud girdles broke a stud at an open track event in 'Vegas, and drove back home 200 miles to L.A. with what he said was a 'tired engine'. Another without a girdle did exactly the same another year, but after working on his motor all weekend with borrowed tools (while others were partying), finally called a tow truck for the same 200+ mile trip. We didn't see him again....
Because they are bulky and interfere with valve adjustment, they are especially recommended for hydraulic (roller) cams that do not need much adjustment. Several shops sell Jo-Mar #1135 for the obsolete Cleveland. They fit under cast aluminum rocker covers if you discard the removable baffles.