It is more about the character of that out of focus area in the image. Some renderings are smooth and soft, others may be more contrasty and harsh looking or holding angular edges. The design and characteristics of the lens has a lot to do with how it renders that out of focus area. For example, I love how my Zeiss 25/2.8 handles the in-focus areas when shooting on my M8, but I find the out of focus areas too contrasty, with too many angular edges and forms. The Noctilux, on the other hand, renders that out of focus area much more softly....almost too soft at times....and that creates a very different kind of separation between in focus subject and out of focus background. The less softened or smoothed background can at time be more distracting to the viewer, depending on the total composition.
I do look at the backgrounds that will appear in things that I shoot, and I try to think about what they may look like in the final image. If very distracting, I then try to shoot more wide open, if possible, to soften that distraction, rather than call attention to it.