....and also blades 'dull' whilst in use and shims can help you tweak a couple more decent shaves from the same blade.I shave daily, I've been using shims for years (I cut off the blade edge off, it takes a few seconds, I have 4-5 shims lying around, haven't cut one in years). A shim has only one purpose and that is to give more blade exposure, it does not change the shaving smoothness of a razor just creates a drop more blade. I have a Wolf 86 which was not efficient enough for me, so I put in a shim which brought the Wolf to a 96, by doing that it became a dream razor for me. I use a shim in my Gillette Old Types ball end and I change out the handles for a Stork aristocrat I get great shaves with this set up. I use a shim in my BBS1 and PAA SS Ascension (using a shim in the Ascension was a bit of a challenge at first). I do not use a shim in my WW1 J series Old type ball end or CG L3 DC, these are perfect for me without a shim.
If I had CG L1 and wanted a level 2 I would use a shim any razor that I like but was not getting the shave I wanted I would try a shim to see if it improve the shaving performance for me. There is no one size fits all in razors not even in adjustable's. If I was using the Feather AS D2 and loved it but wanted it to be more efficient with a drop more blade feel, yet did not wanted to start experimenting by buying razors. I would try a shim and get the next level of efficiency and still keep the smoothness of the shave so, this way I can make a informed decision, do I want to keep this razor or not and I have a better understanding on what I'm looking for, wanting in the shave from a razor.
Experimenting with a shim is a cheap, good and quick way to better understand a razors shaving characteristics and its capabilities and is also a cheap way in becoming a better shaver. Just my opinion.
Bear in mind, I tried this same technique out with several razors and some just do not fit correctly. In particular, any of the razors with plates that are curved will turn out wonky. in short, you can use slimmed down razor blades devoid of any edges and stack them for those. This worked marvelously on my 2 piece Merkur but the blade gap was significant between the bar and the blade. there was no wiggle whatsoever from the blade as the razor is completely shut as normal.That is a lot of blade gap. I personally wouldn't use a washer for a spacer because I want the blade pinched as close to the cutting edge as possible. Last thing I want is the blade vibrating while shaving. I tried the Ming Shi Merkur Futur clone and I didn't care for the way the snap on cap held the blade. Using a washer for a spacer to me would make it feel the same. For shims I just cut the edge off a used blade, about 1/8" or so. I used 4 in the 34c the last time I used it a couple weeks ago and it did pretty good.