I am 7 weeks from a reverse shoulder replacement. I was out of the sling at 5 weeks but actually was doing most things except lifting after 3 weeks. Lifting everything under the weight of a coffee cup was okay. The surgeon said that one reason for using the sling was to remind not to use the arm.

I think it is mainly to keep your arm from being accidentally bumped. I suspect that natural, gentle movement is probably beneficial in returning to better end results, rather than keeping the elbow cranked up all the time, as long as you don't put yourself in situations where you might wrench it. I had an immobilizer instead of a traditional sling, which allowed me to disconnect the wrist strap and use my hand in the forward position, but still kept my elbow strapped to my waist. My surgeon said to keep using my immobilizer when going outside the home for a couple of weeks after discontinuing it at home so that well meaning people would not bump or grab your arm.