This is off by default because people will complain about black borders, but I've tried to keep it to a minimum.
Enabling this option (Screen Offsets in the graphics settings) will allow you to position the screen in games which allow you to do so, maintain correct aspect ratios, and screen shake effects which are done on PCRTC (WipEout Fusion for example) will work.
So to sketch what is an annoying issue is that this for years has been wrongly presented to users.
None Interlacing = Interlacing but if used with a no-interlacing patch it will look like progressive but PCSX2 or really the internal PS2 side only detects interlacing mode. Which blows my mind that the user wouldn't be wrong to assume that None Interlacing = Interlacing.
Weave = Interlacing method (saw-tooth)
Bob = Likely the sharpest but can do vertical bouncing.
Blending = A bit blurry but the most consistent and has no bouncing.
I didn't change the code just the visual presentation to the users.
Example in gif format: https://upload.wikimedia.org/wikipedia/de/1/1e/Interlaced_Animation.gif