Have played with switch barrel rifles for over thirty years.
Have had them on Montana, Remington, Ruger, Sako, Savage, and Weatherby actions.
As stated well by Donovan Moran, there are real economies to having a single rifle share top-of-the-line scopes, triggers, stocks, etc but being able to switch between calibers by only changing the barrel.
There are also economies to having multiple barrels in the same caliber, again stated well by Donovan Moran. Have been in the prairie dog towns and switched amongst a dozen barrels while some barrels cooled and soaked in cleaning solvent.
Use quick-detachable scope rings that are set up to allow easy changing of scopes based on the shooting situation. For example, on one Savage have five scopes -- a 4X Leupold, a 6-24X Sightron, a 8-32X Bushell 4200, a Nightforce, etc taking advantage of different scope reticles, different field-of-views, different weights, etc. Scope settings for a given barrel and load are easily determined and returned to given a good scope with click settings. Some return well enough that you don't even check them on paper in the prairie dog towns, just use the next prairie dog as the confirmation. Would always check the scope setting, maybe with a collimator tool, before going after big game.
Use multiple stocks ranging from lead-weighted benchrest stock to ultra-lightweight synthetic stocks on a single barreled action.
Some switch barrel rifle setups require a barrel wrench, some use a barrel wrench and an action wrench, some use a barrel vise and an action wrench, and some use other tools. John Dustin rifle's barrel wrench can be carried in your pocket.
None that I use require a sophisticated tool for measuring barrel tension or tightness, though some others might recommend it. Hand tight is my approach.
Some setups like the Dustin do not need to have the stock removed to switch barrels. Some of my others do not also. But some do require stock removal. I prefer those that don't.
The rifle below is a left-hand Montana 1999 with 300 Wby, 375 H&H, and 458 Lott barrels allowing one rifle to be a complete three-gun set for Africa. The barrels can be changed in the field,though not between shots at charging cape buffalo).
The rifle in the two pictures below has multiple bolt assemblies allowing a single rifle to shoot cartridges ranging from the 14-221 Walker to the 470 Capstick. Currently have over 100 barrels for it. Can switch barrels in the field in less than five minutes.
Have a Sako setup made by John Dustin that allows field changing in under a couple of minutes.
My largest switch caliber rifle includes a 550 Magnum in its set of barrels.
Switch barrels cannot be defended as a necessity. We really only need two rifles -- a 22 long rifle and a 460 Wby -- and I haven't found a way to switch easily from rimfire to centerfire in a bolt action,know it can be done with the Thompson Contender).
Switch rifles are fun.
