When I grew up in the late 60's, deer were commonly hunted with dogs in East Texas. This area was typically VERY thick brush and shots were close (under 50 yards) and fast!! The most common firearm was a shotgun loaded with buckshot with the few rifles used being open sighted lever actions or pumps.
As time went by, stands began to be used in the morning and evening hours (dogs were run in the middle of the day still) and the advantages of scopes were recognized. The problem was that almost no one (there was ONE outstanding exception in our group) wanted a scoped rifle when running dogs.
The deer were just too hard to pick up quickly in the scope and due to the fact that early scopes were often not as reliable as today.....no one really trusted them to not fail at a critical time. Those early scopes were believed to be fragile and too often tended to fog up in bad weather. Additionally, I don't know how many remember when the crosshairs of scopes were NOT centered, but many times the aiming point was off to one side and above or below center.......not an aid in fast shooting.
For this reason, ALL rifles carried open sights and scopes were mounted to give access to those sights. Various see-through mounts as well as different detachable mounts were popular......but the most used were the "swing" mounts giving instant use of the open sights, but allowing for swinging the scope in place if a standing shot was offered.
I found it interesting when reading an article several years ago (can't remember when or what magazine) where the author tested the repeatability of 8 or 9 different detachable scope mounts (some were VERY expensive too). He stated in the article that he had an older rifle that had the Weaver swing mounts and basically threw it into the test for kicks. Low and behold.....when the dust settled, that old Weaver swing mount beat out every other mount tested.....several times as the author repeated the test to confirm the original results.
I have used the swing mounts for more than 40 years and have never seen one fail or show signs of losing zero. In fact, to me, the Savage 99 just looks right with those mounts in place and I buy up every one I find.
I've actually only "needed" the swing feature a couple of times (mostly due to rain water on the scope lens), but it's good to know it's there......and it does work.
