Yes and no in revolvers.
I carry small frame revolvers when in a revolver mood (about one or two days a week). For me, shooting and carrying any two small frame revolvers of the same barrel length is a very similar experience. The difference in how my Taurus 856UL and S&W 442 shoots is very small, and likely no greater than the experience between two different S&W 442s would be (there is always variation from gun to gun). In carry, a 15-20oz gun feels very similar to me IWB so my steel Taurus 85CH, and aluminum 442 and 856UL feel very similar (the differences are in the bobbed hammer of the 85CH and enclosed hammer 442 vs. the exposed hammer 856), and aren't even that different from my Colt D-frame (in my case a 3" new model King Cobra). For pocket carry, the smaller dimensions of the 442 are noticeable over the 6 shot 856UL, but both are quite pocketable. So, I very much do have functional spares in this category, and I will likely add a Taurus 856 Defender or 905 Defender (9mm) so I have a pair of 3" small frame revolvers.
No true spares for autos (for the most part), but I have some functional spares.
I have multiple carry guns, or guns I intended to be carry guns, in different sizes for different needs. That worked when I couldn't carry much and only carried about once a month when out of state on a non-resident permit. Now that I could finally get a MD permit post-Bruen, I find that I've narrowed down the pistols I actually carry, and I'm thinking strongly of getting a spare (either a true spare, or second in the same category/functional spare).
I'm phasing out my M&P40c, that middle ground between 10+ round micro-9 and compact service pistol just doesn't work for me. It is big and heavy enough over the micro-9 that I don't like carrying it over my SIG P365, and it isn't small enough over my CZ PCR or Glock 19 to carry any advantage over just carrying the bigger gun. I do have functional spares in the compact service pistol category: a CZ PCR, a CZ P01, a CZ 75 Compact (steel, only a range gun, but the practice carries over nicely to the aluminum versions), and a Glock 19. Even with the weight difference between the PCR/P01 and the G19, I find very little difference in ease of carry on my belt. For range practice, my full sized CZ 75B and full sized Glock 22 are close enough in experience to the PCR/P01 and G19 for the range practice to transfer over well. If something ever happens to one, I'm still well covered (even if I sell one of the compact CZs), and I can get plenty of practice without dirtying my carry gun.
I need to do similar for my SIG P365. I don't clean my range guns often, I want to shoot my carry regularly, and I don't want to carry a dirty gun. That alone is a good argument for a second 10+ round Micro-9 (one to carry, one to shoot, and switch off every couple months). Further, my Taurus 856 recently experienced my first squib load, one that partially remained in the cylinder and was partially in the barrel, locking up the gun. I didn't want to look down the barrel of a loaded gun while removing the squib, so I left it with a gunsmith to deal with. If I didn't have the choices in small framed revolvers I already mentioned, I'd be without a lightweight snub for pocket carry, but I wasn't. I realize, if something puts my P365 out of commission, while I certainly could carry a larger gun for an extended time, I'd rather have the choice of my preferred carry size while waiting for it to be fixed. The only thing I haven't decided for sure is if I get another P365, or if I get a Shield Plus, G43x, or G48. Just when I think I've about decided, I start thinking about the alternative. So, I'm still unsure if I'm getting a spare, or just a functional spare.