To the OP:
In a perfect world an action (or any product) stays "put" once it's been machined.
Now for a dose of the real world. I'll use a few examples from different industries to help illustrate.
Years ago all I wanted to do was work as a racing engine machinist/builder on NHRA Comp Eliminator and Pro Stock engines. Being in S. Cal as a Marine at the time I had a good base of engine builders to learn from. One of the best was a guy named Richard Conley. 2.52hp per cubic inch on pushrods, carbs and gasoline in the early 90's was a force to reckon with in C Altered. (7 national records)
One of the things I learned quickly was the bore finish and dimensional stability was/is EVERYTHING with these little buggers.
We'd run a motor on the dyno and then tear it down to kiss the bores with the hone. The reason was the material (cast iron) shifted around after a few heat cycles. This is why years ago circle track racers would almost pimp their own mothers for used dragster engine cases. The hundreds of heat cycles done a 1/4 mile at a time meant for a very dimensionally stable casting. Perfect for an endurance type engine.
Another example. In the machining trade it used to be pretty common to take on an apprentice. One of the first thing the student would do was locate a chunk of tool grade steel and then chuck it out the back door for a couple years out in the elements. The material would "season" over a time; meaning the cycles of hot/cold from day to night and with summer/winter would slowly stress relieve and stabilize the material. Once the "old fart" decided the student had enough experience he'd be instructed to go find that piece of material and make a tool maker's vise from it. Made properly they are very precision tools very useful for set ups and work holding. The point is the material wouldn't have stayed "put" if it were made out right out the gate from the foundry.
Modern example. One of the most challenging products to make for firearms is a nice floor metal. You have a lot of thin walled features that invite tool chatter and require a bit of creativity to properly fixture and support while cutting. Some of the really nice ones are 100% one piece and made from solid bar stock material. If the material is purchased as round stock rather than plate there's a better chance of the stuff retaining dimensional stability. It's just because of how the material is formed at the foundry.
Now for gun stuff:
Any premium/quality made receiver is going to begin life as a piece of tool/aerospace grade material. It's going to be heat treated to around 45 Rockwell C. (depending on the material (chromo/SS) the scale used to check hardness can be different, but essentially they are all after the same thing; hard enough to deliver sufficient tensile strength and lubricity while soft enough to avoid being susceptible to fracturing)
Your question can largely depend on the firearm's application, use, care, and choice of cartridge.
Case in point: I once worked as a manager for Nesika and Dakota Arms. The Dakota model 76 is a fine action manufactured from premium grade aerospace certified materials. If the action is chambered in a 223 Remington its very unlikely it will ever need to be touched again. If however the customer wants a 416 Rigby or 338 Lapua Magnum its not uncommon or alarming to see that gun come back in 5 or ten years for a headspace issue due to the lugs yielding a bit. Sooner if the owner is an avid shooter.
It's not nearly as terrifying as it sounds.
If we go buy a brand new shiny framing hammer that's well made and case hardened it's not too tough to envision the impact surface being peened and deformed after years of sinking nails into 2x4's. A framing nail is maybe 20 Rockwell at best. The hammer face is likely to be in the upper 40's to low 50's. How does a butter soft nail do this? 1000's upon 1000's of impacts is how.
Now that's just a nail being driven by the force of a man's arm. Compare that to the tens of thousands of pounds of pressure developed by any modern centerfire cartridge. It's impressive that the guns last as long as they do.
So, back to your question: You "tune up" an action if/when there is a reduction in performance (that can be conclusively traced to an action problem) or when there is a safety issue/concern (such as a gun going out of headspace)
Is it something a guy needs to dwell and brood over? In 99.9% of instances NO it isn't. If however you have a 375 H/H magnum that's 20 years old that you shoot the dickens out of and your cases today are .015" longer than the ones from 15 years ago then it'd probably be in your best interest to send the thing to someone with the right equipment/experience to inspect/repair it and make it a safe and function piece of equipment again.
What I hope you take from this is there isn't a conclusive, etched in stone answer to this question. (which is very good btw, much more interesting to talk about than what color shoe polish to use as a release agent for bedding
) Statements that an action never needs to be touched again is a bold claim that can potentially get a guy in serious trouble down the road. (meaning litigation and/or the Emergency room) I've seen otherwise and am fortunate to have been around a lot of guns in the last 12 years.
Hope this helped.