Comment 6 for bug 1404745

The problem is still relevant.

https://www.freebsd.org/cgi/man.cgi?growfs(8)
  -y ``Expert mode''. Usually growfs will ask you if you took a
      backup of your data before and will do some tests whether special
      is currently mounted or whether there are any active snapshots on
      the file system specified. This will be suppressed. So use this
      option with great care!

Without this option FS doesn't resize.