Persons often write " Mods, feel free to move it if necessary." Do the mods give consideration to permission?
The mods will move it regardless of our wishes unless, for example, someone starts a thread on a contentious subject in GD and asks that if at all possible, it remain there rather than get moved to the pit and become acrimonious.
Mostly, I think what people are saying with “move if necessary,” is “I’m not sure which forum this topic fits best in so I’m just going to pick one but if someone thinks it will go better elsewhere, by all means, I don’t have my heart set on here.”
I report posts which say “move if neccessary” and don’t mention it in the thread.
I’ll sometimes offer my opinion on whether moving is desirable, but usually, I just feel strongly that if anyone writes stuff like “move if necessary” it needs to be seen by a mod, and since I don’t assume that mods read all posts–especially in a speedy manner.
I’ve also been known to report threads that I think are in the wrong forum–especially advice seekers not in IMHO.
It seems superfluous.
Which is why I proposed TSOPDA (The Standard OP Disclaimers Apply) back in 2005. Of course, it didn’t catch on 
We’ll move threads we feel are in the wrong forum based on our own judgement. Personally, I feel that this kind of disclaimer is polite rather than necessary.
Like Colibri, I regard it as a courtesy disclaimer – as Inner Stickler notes, it often seems to mean “this could have gone in a couple of places, and this forum won the coin flip.”
We in General Questions appreciate it.
I always view it as a polite way for the OP to note, in advance, that they are not going to have a hissy fit if we deem it advisable to move it. It has no affect on my decision to move a thread, but I appreciate that they have made the gesture to abide by a difference of opinion regarding a thread’s placement.
The flip side of this, of course, is that it is extremely rare for me to view the placement of a thread as either a hostile act or a stupid one.
About the time that I have moved multiple separate threads on the same topic by the same poster to the same destination with the same explanation for the move, I am liable to begin thinking that that poster is playing some silly game to attract attention or that they really are not amongour brightest members. However, anyone can have an off day. For that matter, it is a truism that we do not easily see how our words will be perceived by others, (hence the employment and job security of editors), so I am not influenced by appeals to leavea thread in place if it seems, to me, to have a better fit in a different forum nor does the OP’s acknowledgment that it might have a better location alter my views.
And don’t forget newer board members who might not be too clear on the dividing line between, for example, General Questions and IMHO, and are basically saying “I don’t know if I made the right call here, please feel free to correct me and we’ll all hope I get it right next time”. 
Mods, please move this post if it’s in the wrong thread. Thanks!
It’s just a friendly way of saying “I wasn’t quite sure where to put this,” and is meant to soften the blow if the thread is moved. When you start a thread that is abruptly hit with “This belongs in MPSIMS. Moved.” it can feel a little brusque even if it was absolutely the right call. Admitting it before hand is akin to saying “Hey, I know the rules and the different forums and all that, but this one was a tough call so I put it here, but I’m not attached to it or anything.” It’s not really about giving the mods permission, but about letting the readers know you know what’s up (at least usually), not letting the thread get hijacked with talk about the move, and perhaps premptively defending against your own ego if what you were hoping to be a great GD ends up in IMHO.
That’d be hilarious if they did…
I shall take that up. I intend to become aware of all SDMB traditions.
I’d use it as Inner Stickler suggested, sort of “I did my best to determine which forum this belongs in; don’t hold it against me if I’m wrong.”