I have been using a Caldwell led sled, for 6+ years. Load developed for over 30 rifles in multiple disciplines, Silhouette, PRS, F-TR, Service rifle etc. I really do shootmore

. Well Junior and I do so typically were building two or more rifles for each discipline. We have our own machine shop, a trade I picked up 35 years ago. We chamber our own barrels. Make a lot of our own parts.
We never hang anything off the barrel and never strap down a rifle during load development. That would change the barrel harmonics. Sometimes we add sand bags to the sled sometimes not but are always consistent for that rifle while searching for that elusive single hole load. See the Lab Radar in the picture. We use it for velocity at the muzzle and using an electronic target down range that measures POI FPS we compare and seek similar trends while doing ladder analysis.
We do get consistent results load developing this way. First we ladder test at 500 yards, then OCW at 100 yards, then jump test at 100 yards. This method has produced match winning rifles. Rifles that have beaten all comers in our state at least once. Junior has broken six NRA national records. Point is I think we are doing a few things right. First is starting with a rifle, and load up to the task of shooting a perfect score.
I read this thread because I questioned my methods having watched an old bench-rest shooter for years always using just a bag and a bi-pod with good results. Then I realized that his entire rig is set up for that. I have concluded that by taking as much of the human variable out (using the sled) we end up with more consistent results.
Having done extensive testing on so many rifles I have found that some of my skills improve while testing using the sled. For example, NPA, breathing, trigger control and overall ability to focus on each and every shot for 100+ shots. Yeah go out and shoot 180 rounds in a session 3 or 4x a month. That will do it. It is not a replacement for slinging up prone or offhand practice but over the years I do accredit some of my skill improvements to the added trigger time while load developing using the sled.