One very need feature for users of longer lenses, is that many times you DON’T want the Magnified view to cancel when you 1/2 press the shutter. This could useful when you are tracking a bird or other smaller objects (subjects) with a manual focus lens, and want to keep the magnified view during the shutter trip.
This also useful with Native m4/3 AF Lenses in certain situations.
On page 88 of the Olympus OMD E-M5 PDF manual.
Go to the “Settings”, “Custom Menu”, D”, “LV Closeup Mode”, “Mode 2”