Is there a word or phrase that describes the act of saying something for the sake of it?
To bloviate, or "speak or discourse at length in a pompous or boastful manner" is not exactly what you want, but it is a practice of those who "speak for the sake of saying something". Bloviate and bloviation have the right sound and connotations for speaking done for its own sake. Example: "His lexiphanic speech was a marvel of bloviation and bombast."
Previous answers have mentioned many words, but seem to have left out babble ("idle talk; senseless prattle; gabble; twaddle") and logorrhea ("an excessive and often uncontrollable flow of words" or "excessive talkativeness").
In an alternative interpretation to that required by the question, a speaker might speak because of liking how he or she sounds; this suggest the adjective euphonious ("pleasant-sounding; agreeable to the ear; possessing or demonstrating euphony") or noun euphony.
Another word unsuitable as an answer is sententious, although it has the look and sound of a word that ought to be appropriate. In fact it has in one sense the opposite meaning: "Using as few words as possible; pithy and concise." Another sense of it, "Tending to use aphorisms or maxims, especially given to trite moralizing" might actually be relevant; much speech at length is empty or trite moralizing.
While not a technical description of the act you describe, I can think of several terms that seem to fit the context you are implying (based on your comment on Barrie England's answer) — Descriptors of someone who "likes the sound of their own voice", or of such a person's speech
"Blather" and "Prattle" both express voluble, empty speech, as do "Chatter" and "Prate". There's also "Palaver", but that has a less insulting connotation, and some definitions that do not fit this situation.
For the person who blathers or prattles, they may be "Pedantic", or tend to "Harangue" unnecessarily.
There's a bunch of words you might use, depending on the specific circumstances.
One good fit may be "plugging", which could describe both the act of repeating a point excessively as well as the type of self-promotion you described in your response to Barrie England.
Other possibilities could include "embellishing", "stretching", "showboating", "grandstanding", "prating", "prattling", and "preening".
The speech itself could be described as "rodomontade".
You might describe a person who partakes in this behavior as "big-headed", "patronizing", or "ego-centric".
something of no consequence: The book is pure fluff, but fun to read.
fluff v.; fluff-up
Informally, you could call it stuffing, as in material used in packaging. Some smart companies may make a 'surprise offer': delivery containing only the stuffing. Some speakers and some writers do it all the time.
It might be called claptrap, particularly if it's political talk.
Just another thought:
Platitude -- A trite, meaningless, or prosaic statement, generally directed at quelling social, emotional, or cognitive unease. The word derives from plat, French word for "flat." Platitudes are geared towards presenting a shallow, unifying wisdom over a difficult topic. However, they are too overused and general to be anything more than undirected statements with ultimately little meaningful contribution towards a solution.
He speaks in platitudes, saying much yet, nothing.