Note that it’s perpetuated incorrect information, free testosterone is responsible for several effects, but total is equally if not more important aa SHBG and albumine binding isn’t just to “stop” testosterone action, they also perform transport, have cellular effects, literally help body to hold on testosterone. Body can regulate SHBG efficiently keeping free testosterone not low enough for a person to crash, while total could be barely in range or even lower and a lot of physical symptoms will be present, just not felt acutely.
Using free testosterone as additive metric if total looks good on paper is a way to go, but there’s no justification to say that a person is “normal” if their free testosterone looks good, but total is low, while many try to use it in this reverse way.