"I have gathered a posie of other men’s flowers, and nothing but the thread that binds them is mine own." -- John Bartlett, if one believes Bartleby.com or Michel de Montaigne, otherwise.

Quotations can emphasize an idea or restate it pithily or to set the stage for a chapter. This sort of quote is often used in textbooks, as well as in popular books to introduce scholarly topics to the lay public. For example, I'm in my office at work now and the first book I pick up is "Principles of Artificial Intelligence" by Joscha Bach. I have not read this book yet, but it is here on the shelf waiting for me. I turn to the start of a random chapter somewhere in the middle, and I find a quote from John McCarthy (among the first AI researchers).

At other times they convey irony directly (or indirectly in the manner the quote is juxtaposed by quoter). I cannot recall a specific instance of seeing this sort of quote and only have the vaguest sense that I must have seen such a thing once or twice. Even if this fuzzy recollection is not a confabulation, this sort of quotation must be relatively rare in comparison to the other kinds.

Sometimes quotes are misused or misapplied. Quotes are termed "out of context" when, for example, they are cited in such a manner as to indicate a point other than that intended by the original author. One is led to believe that lawyers are fond of this. Often quotes out of context are used to make it appear that the person quoted has espoused something exactly contrary to what he attempts to convey. (Example: attempts to show that Darwin believed the eye could not possibly have evolved or that the fossil record disproved evolution.)

In other cases, quotes are used like slogans. We all agree that Mr. A is a wise man. Mr. A said X is true. Therefore, X is true, because he was a wise man. I will give no example of this, but I can think of several as I type this. In many cases, like this quotes can become slogans or "talking points." I suppose G. Lakoff would say that these quote /slogans are successful examples of "framing."

Scholarly works often use quotes rather than a mere citation or reference to another person's work. Maybe the wording seems so clear that the borrowing author doesn't want to spoil the original intent.

A critique or review, though, might quote every line or couplet of a poem to dissect it in the body of text.

Quotations can be used in lieu of thinking, or even to obviate thinking, or they can be used to focus or direct thinking.

I don't see how quoting can be a bad or a good thing any more than writing itself is a bad or a good thing. Rather, there are good an bad examples of each.