@muratmaga The thing about resizing the effect groupbox that goes against some of the negatives talked about previous is that effect buttons would move location when this is resized. If effect buttons should be in the same location for familiarity then this dynamic resize/reorder would go against that idea. If you make it more columns or less columns, then you have to relearn where the expected location of the button is at.
Having a strict grid layout would make sure the buttons are always in the same place and you would scroll down if your screen size was too small to fit them all.
I guess for custom app purposes if you set only say 6 effects to be visible, then not sure if the 3 rows by 2 columns is still valid or if the user would then want 6 rows 1 column. So maybe adjustable as a setting for at least the custom app purposes. Though the custom app developer could probably change the layout to fit their purpose anyway rather than Slicer developers trying to guess what they might want in their custom app.
Regular unmodified Slicer would probably benefit with it always being a 2 column setup.
Thanks to all the efforts of @jamesobutler, the new Segment Editor layout is now ready - see more information (and provide any feedback and suggestions) in this topic: