It took a long time for us to exhaust our small original supply of spare parts from when we started using 3rd gen guns, back when they were first released.
The mostly easily lost parts (small springs & plungers) are handy to have for when they disappear from the bench top.
Some of the smaller springs, like those used under the rear sight base, can experience damage if someone is inattentive when installing the rear sight base, and it helps to have extras. I've noticed some differences (revisions, likely) in them over the years.
The firing pin safety levers can be different among some models.
I've seen a few firing pin springs become shortened from use over time, and I've even come across a bent firing pin.
Over the years I saw us replace a steadily increasing number of parts as the well used (and abused) guns started to reach 12-20 years in-service. Replacement of extractors & ejectors outnumbered drawbars, hammers, sideplates, slide stops & guide rods, but even then the numbers of damaged, broken & worn parts weren't what you might call large (and we had about 500 of the older guns). Well-used pistols can require periodic replacement of some parts which typically wear as the result of normal shooting. Not unexpected.
Probably not something that's going to happen to the average owner who may not ever shoot more than 500 rounds through a particular gun, though.
I think I replaced an extractor in one of the issued guns I used over the years at about the 12,000 round point, and I wasn't the first person to whom the gun had been issued. One fellow from the factory once told me that extractors might sometimes become work-hardened and brittle after about 10 years or 10,000 rounds of usage, becoming susceptible to chipping or breakage, but that's only a rough guesstimate and some guns might well run longer. Naturally, abusing extractors, like loading the chamber by dropping around into it, instead of loading from a magazine (as intended), might damage extractors and require replacement sooner than normal wear & tear. (Extractors typically require fitting, and gauges to check for fit & tolerance, though, and aren't what you might consider 'hobbyist/enthusiast' replacement parts.)
Armorers are told to replace a sideplate once the pin becomes loose from the plate (so it can be turned with light fingertip pressure), and to replace guide rod assemblies when the staking of the guide rod collars becomes loose so the collar can easily be turned within the rod body. (Newer design guide rod assemblies started to incorporate the 1-piece rods which didn't have a separate collar staked in them.)
Ejectors have been revised over the years to eliminate the sharp angle under the back of the tip, which helped eliminate a potential stress riser and helped prevent tip breakage. The tips were also lengthened to speed up ejection of the empty cases. (Part number can vary by model.)
There are some differences among some of the ejectors nowadays when it comes to models/calibers, so it's best to check with S&W to confirm a part number.
I've collected a lot of the different extractor springs over the years to make sure I can find one for repair/replacement in various models & calibers. Also, extractor revisions have occurred since the early 3rd gen guns were introduced.
Replacing recoil (and mag) springs periodically can really help reduce the battering effect of recoil forces, and making sure the gun is properly cleaned and lubricated helps extend useful service life, too.
Just my thoughts.