Searching for line beginning

[Eli Zaretskii <eliz@gnu.org>]

C-a (move-beginning-of-line) does this to find the line's beginning:

    ;; Move to beginning-of-line, ignoring fields and invisible text.
    (skip-chars-backward "^\n")
    (while (and (not (bobp)) (invisible-p (1- (point))))
      (goto-char (previous-char-property-change (point)))
      (skip-chars-backward "^\n"))

Apart of the fields part (which can be handled by binding
inhibit-field-text-motion), can anyone see a reason why not use
line-beginning-position instead?  The latter is much faster,
especially when lines are very long.