Piggybacking a Refrator to an SCT

If I want to piggyback an ST-80, is there any reason I need to line up
it's sight with that of the Main scope? (I have a Meade LX90.) Only
reason I can think of is if I want to image with the short tube while
viewing the same object through the main scope (or visa vera). Is
there any other reason? Also, do the mounting brackets allow for
fine-tuning of the ST-80 (up-down, right-left) so that I CAN align it
to the main scope?

Thanks!

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