Hmm, in my view there is a difference between the original proposal and using an amemdment to any of the .profile or .xsession files: It is quite reasonable to assume that a user starts the X-server more than once, or (especially with 'multivt' now an option) a user does login more than once. In this case the events would get executed again, which might not be the intension of the user.
The way I understand it '/opt/bootsync.sh' and '/opt/bootlocal.sh' would be only run as part of the boot process. Which is different from the other options mentioned above.