When I place a image or a map by using a Roll20 tab, it appears placed to the upper-left part of the screen (when it is not larger, by zooming or by default image size, than the available display area).
This can be inconvenient because the vertical options bar is always above the image or tab content. Another issue is that you can't offer a "centered" image to the players: it appears aligned to the upper-left part of the browser screen, which diminishes the effect of some backgrounds and visual representations.
Hence I think that it would be a good idea to be able to change the placement of the tab content, maybe by being able to dragging and moving it around, like it's currently possible to do with Handouts. This would be useful for maps as well, allowing to center them inside the display area, or to put them where is better for you, along with Handouts, Turn tracker and other things that Roll20 has.
Perhaps the visual alignment of the tab's content can be addressed by adding options to "Page Settings".
Also, ideally, the chat box could be moveable (I'm aware that such area can be stretched horizontally), and the vertical options bar too. That would add more flexibility to Roll20 as well.
Roll20 off-centered image-background shared with players:
