Does the option really belong in echo? Who knows, but it's certainly been useful to me.
UNIX fifth edition goes for absolute minimalism. Echo in Plan 9 is apparently used enough that it's worthwhile to optimize the number of times write is called. FreeBSD echo looks like someone just learned about writev. OpenBSD's seem like the sanest of the minimalists.
What's the takeaway for you?
For many people, from the writers of the Single Unix Specification to the Debian Policy people, the take-away was and is use printf, for nigh on 20 years now.
$ printf "This\tis an\nexample\n"
This is an
$ printf "This is %-20s example\n" another
This is another example