The basic sense is as Glasguensis says. So in general it means 'I offer you this opinion/piece of information and you will determine its worth and respond according to the value you attach to it' ; it may EITHER suggests a modest uncertainty on the part of the speaker about the value of what they're offering OR the speaker's feeling that what they have to say won't be considered by their interlocutor to be of much value (the context, and tone in speech, usually enable you to determine which of these two possibilities is most prominent; lingobingo has already interpreted your quoted sentence.)But what I still can't understand, in sentence like this, is it used to let know the modesty of nurses' opinion, or of the one's who says this.
No, it doesn't, or isn't. I wasn't suggesting uncertainty about the validity of the information/opinion offered , but about its value. If someone is offering information , they believe it is true and are asserting it as fact ; what they are not sure about is whether the person they're offering it to will find it helpful or useful ; and sometimes they may be suggesting that they're doubtful themselves about whether the information is likely to be helpful or useful, but they're offering it just in case.he main point I try to understand is if underlined orange part follows on from "for what it's worth" or, in other words, is an extension of the sense that lies in "for what it's worth". I conclude it might be so from this understanding, if you are not certain how valid is piece of information you provide, then you obviously don't know exactly what happened there.