Blur is important in how it relates to what's in focus: is it a supportive background? is it blurred enough not to compete with the subject? are there conflicting colours? etc. etc.
Bokeh, in the sense of the quality of out-of-focus rendering, isn't usually a dealbreaker, but it can help make a photograph with a less distracting background. The worst case here, for 99% of tastes, is mirror-lens doughnut bokeh.
Also, if you have, say, a typical cafe shot of your companion across the table, and a waiter is blurred a couple of tables away in the background, it makes a difference whether:
- the waiter is still fairly sharp and competes for attention with the sharp, in-focus subject
- the waiter is 'nicely' blurred (to your taste)
- the waiter is blurred enough to form a pleasing , recognisable gooey shape
- the waiter is so blurred he forms a shape that melts into the table and ends up looking pictorially distracting ("I can just make out something in the background, but it looks like a giant spider")
-the waiter is completely blown out, with the result there's a large blob of colour you didn't expect that detracts from your companion
Using an RF, of course, there's some unpredictability to this.
I've had photos where I've felt the bokeh (in the sense of blur quality) was a dealbreaker, usually where a row of ceiling spotlights has turned into double-lined pentagons. In a photo of something straight, like a stepladder, this might be okay, but with a photo of something rounded, like a person, this seems to set up a tension. Though this is mainly because the lights are so bright against a dark background, which brings us back to how blur interacts with the subject.
