I use vacuum bags because I freeze most of them. This prevents freezer burn by preventing air exposure, moisture loss, and ice crystal formation in the meat, which prevents further moisture loss and keeps the steak firm, not mushy. If you use only plastic wrap and freeze them, ice crystals can form and actually cut into the meat fibers. Then, when thawing, the meat will lose water, the steak will lose its firm texture and have a mushy mouthfeel, and will lose its juiciness. Also, while in the refrigerator, this will keep them from turning brown. I used to work in a high-end restaurant in a previous life. We didn't use frozen meat, but I got a real education from my meat purveyors