Great thing about Fowler, in addition to his puncturing the balloons of the pretentious, is that he always sticks to the language the way it is spoken or the way it is written by those with common sense.
Most copyeditors will shift the word "only" to its logical place in the sentence, but Fowler says sometimes it is earlier than its logical place as a kind of signal to what the rest of the sentence is going to say. Compare "I gave him only five dollars" with "I only gave him five dollars." The second is less logical but more colloquial and therefore easier to read.
Don’t confuse, “Once, I went there” with “I once went there.”
And, especially, don’t confuse “habitually” with “used to.”