We learn in this course that plural endings are optional. So "loD" here can mean either "man" or "men", and "be'" can mean "woman" or "women". Are plural endings in Klingon generally only used when necessary to avoid misunderstanding? Or are they more common for some nouns than for others? Or more common in formal contexts, perhaps?
You may find that different klingonists have different usage frequencies. In writing you will mostly find them not used if context and prefixes make it clear. You will mostly find them used when neither the context nor the prefix make it clear. I get the impression that they are used more in talking, since it's easier to use them than to stop and consider if the context has made it clear. In any case, some people use them more and some people use them less, but there is not a difference for particular words or a formality difference.
To be clear: there is no KNOWN pattern to how frequently Klingons drop plural suffixes. There may be differences among different groups, but we haven't been told what they may be. We do not know that there is no difference; this is not something that Marc Okrand has said.
(He HAS told us usage patterns of other language features. For instance, young Klingons are more likely to shorten doubled consonants into a single consonant, while older Klingons are more likely to pronounce them longer, or even doubled. So an older Klingon is more likely to pronounce toDDuj rescue ship by holding the D a little longer than usual, or even by pronouncing it twice, while a younger Klingon is more likely to pronounce it like toDuj courage.)
That's fine, but I don't think that's what La_Mariette was asking about. The focus is not "How do other people learning Klingon choose to use plurals?" it's "How are plurals supposed to be used?" And the answer to that is, we don't know. Though it would make an interesting paper to survey all the known canon...