They don't receive all the benefits, only their percentage ownership. If they own 10% and later down the road sell the subsidiary (or the subsidiary sells out or merges with someone else), they will benefit only to the extent of the 10%. The other 90% shareholders will benefit from the rest.
When they own, say 10%, and the subsidiary is leveraged 10 times, they do not "control" the entire asset. They only "control" the 10% that they own.
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