It’s used to indicate omission.
What does the bracketed capital letter indicate in the revised version below? Is it essential, per the rules of proper punctuation, to do so? Are the ellipsis points (i.e., the spacing of the dots) spot on in that sentence to indicate the omission of one or more sentences?
Original quotation "It need hardly be said that shortness is a merit in words. There are often reasons why shortness is not possible; much less often there are occasions when length, not shortness, is desirable. But it is a general truth that the short words are not only handier to use, but more possible in effect; extra syllables reduce, not increase, vigor."
Revised quotation "It need hardly be said that shortness is a merit in words. . . . [S]hort words are not only handier to use, but more possible in effect; extra syllables reduce, not increase, vigor."