To me, it has become really important to not rely on composing with a shallow depth of field. It can become a crutch in ways, especially as you are learning how to deal with it, and the rangefinder gives you to facility to see all of the elements in focus as they will be placed in your frame, regardless of whether you have elected to include or exclude them from the focal plane. That is calculated as an extra measure of composition in your head, but it doesn't tend to distract like it can with a through-the-lens viewfinder such as in SLRs.
One of the other benefits of having a viewfinder on the side of the camera is that by design, your face is still showing (unless you shoot with your left eye, of course). With a rangefinder, I don't feel like I'm hiding my face behind the camera body. It's a fluffy issue, but one that I do I prefer now that I've used those types of cameras for so long now. It's probably why the new Mamiya 7 medium format film camera I bought feels so natural to use.
And finally, the lens are so tiny. Gone are the days of wielding enormous SLR lenses. Even the Sony mirrorless FE lenses are as big as a DSLR. It didn't take long for me to get used to a 35mm lens that was the size of golf ball.