If you are shooting slide film, you'll notice the difference with and without the filter, using a 90/8 S-A on 6x17 (I used the same lens with a Da-Yi 6x17 back). At that point, it's a matter of taste, lighting, and how important the detail is at the edges of the frame. If the main subject is in the center of the frame, then some falloff can make a stronger composition. If you want to put the subject at the edge of the frame or make a more narrative image that reads from left to right, a center filter gives you more options.