When closing a window, the windows are rearranged. When closing multiple windows in one go (probably not an uncommon scenario), this breaks the mental flow and slows down the process.
In my opinion (tm), closing a window should simply not trigger a re-layout. Maybe make it an option!
While the windows become larger as some are closed, and it becomes easier to identify what's in each window, every time they change position the user has to perform another visual scan of all windows to tell what's what.
Windows that were already identified when the effect is first invoked have to be visually re-scanned and mentally re-processed once they move, and this repeats for every window closed. The cognitive workload increases much more than any benefit one might get from having the windows get bigger.
Seems it was discussed in 2013, but is still open:
*** This bug has been marked as a duplicate of bug 315314 ***