I made a point of walking up the hill (?!) behind the Sassafras benchmark recently, and I most likely won't be satisfied at the wrong end of Rainier's crater. I got worried atop Rogers, since I thought there was a sign (there isn't anymore). It wasn't until I sat down for a break on that conveniently placed boulder that I noticed the benchmark. I guess I don't have a rule of thumb, but safety (no standing on cornices) and practicality (midnight at Brasstown means no ranger-assisted access to the benchmark) rule.