The idea was to address a long-standing issue with Smalltalk devlelopment; unnecessary window proliferation.W
One nice thing about that preference is you can easily tell when two objects refer to the same object. By inspecting the reference from the first place, you get the inspector window, then inspect it from the second place, did it open a new window? (different reference) or re-top the original inspector (same reference)?
The benefit is clear and tangible, and there are mutiple ways to get multiple browsers onto the same object even when the preference is set. Why would you be annoyed by less redundancy?