Is it true that "set off for [some destination]" is more common than "set off from [some origin]"?
Both are perfectly legal and frequent. But for the sake of conversation:
The context of "set off" is usually going on an adventure. When going on an adventure, one is usually thinking about the future...and this new place. So if you had to pick just one place to mention, you're probably going to mention the new place.
If your emphasis is on the place you're leaving, then "set off" is less likely what you'd pick. There might be a reason where you were going was not important: "They fled from Ireland"
So in usage, "setting off" for a destination is probably more commonly used.
Note that although Google says:
- "set off for" - About 5,930,000 results (0.47 seconds)
- "set off from" - About 5,240,000 results (0.74 seconds)
The phrase "set off from" has a very common usage, meaning "distanced from". So the text of a page can be "set off from" the edge of a page by a margin, or a person can be "set off from" the competition by their unique qualities. I'd imagine a fair number of "set off from" references come from that, while "set off for" only has the purpose asked about in this question.
(Excluding things like "he was set off for a while", which indicates something made someone mad for a while.)