Generally the theory is the higher % held by institutions the more volume will be transacted as Institutions ENTER or EXIT positions of the stock. Thus a institutions transactions will trend for a few days as the institution positions itself, as large positions take days to be filled to the required investment size of the institutions.
The higher the better for possible trending
This is subjective and different traders have different % amt. I like 75%, but have no way to say that this is "right".