Since there are two opposing camps on this topic (it has been this way for as long as I've been into audio), it really doesn't matter one way or another. If you have heard a difference, it won't influence the other camp one iota, and vice-versa. All in all, it's a moot point. I mean, who really cares one way or another? But I raise an eyebrow when I read uncompromising words such as, "always" and "never".
Reviewers usually allow 8 to 12 hours of "break in" before reviewing speakers or subwoofers. Is it necessary? Perhaps and perhaps not. Different surround material may take longer to break in. I couldn't get much sound from a BIC subwoofer I received as a Christmas gift for the first few hours (thought it was a bad sub). Steadily, over time (a few weeks) it seem to hit its stride. People can believe this or not. Makes no difference to me. I also suspect that for most speakers, one won't hear much of a difference, if any, between the first ten minutes and ten days later (I didn't on the EMP Tek R5Bi's). Not that speaker sound won't change over time, it very well may. But I doubt our ears could measure this minute, steady difference. Although if we had a speaker that has been used for a year, then bought a brand new pair, I suspect the difference would be readily audible.
Full panel speakers such as on my Maggies are quite different (mainly the bass panels). It's not that I had to baby these speakers, it just took a few months to stretch out the mylar panels to get the depth I had heard at the audio store. Had nothing to do with quality of sound.
As to the question if one needs to break in a speaker, I'd say it depends.
Music area: Magnepan 3.6, McIntosh MC2205 amp & C48 preamp, SVS SB13-Ultra, Oppo BDP 95, dbx 3BX, and assorted equipment.
Movie area: EMP Tek E5Bi (were rebadged to R5Bi), RBH/EMP Tek R55Ti, PSA S3000i, Denon X2000, Oppo BDP 83.