I suspect, based on the way you have described the options, the difference is less about hot swapping, and more that when you use a Tiled layout (all of equal size), then all the games are rendered internally at a smaller resolution than when you run the games with 1 large and 7 smaller windows.
Note: all resolutions/sizes below are based on a reference monitor resolution of 3800x1600.
i.e. if I took a punt and said you have 1 in the top left and 7 around in a reverse L in a swapping layout, then the default way ISBoxer will set this up is that all games would be internally Rendered at 3040x1280. So rendering a total of 31,129,600 pixels across 8 games. The smaller windows are scaled down for
display purposes while being rendered at the full size of the main region.
This is so if you do swap between windows and bring a small region to the main region then the games do not resize their rendering, which can sometimes take several seconds depending on how the game handles this, and also so action bars line up (the game UI scale usually does not change with the render resolution).

If you chose a tiled layout then all games are being rendered at 1280x533 for a total of 5,457,920 pixels across 8 games. This is almost 1/6 the amount of pixels of the corner layout and thus requires less GPU processing power to render. This is not because Swapping is disabled. You could have a tiled layout with swapping, however, this is not intuitive so by default swapping is not enabled for a tiled layout. With a tiled layout ISBoxer has no need to keep all the games internal render resolution in sync to a main window to prevent the graphics reset when they do swap because with a tiled layout they already are in sync as all the windows are the same resolution.

If you want a large window with the smaller windows rendering at their display resolution, then you can get this by changing the Instant Swapping to False. This will result in the large window rendering at 3040x1280 and the 7 smaller windows all rendering at 760x320. This all totals 5,593,600 pixels across the 8 games.

You can still swap with this setup but if you do then it will cause a graphics reset in the game which may change your game UI positions around, will be slow, and might result in mouse broadcasting not lining up (this may not matter to you; it can also potentially be worked around using a Scaled cursor positioning mode in the Repeater Profile). You can also set the Enable Swapping option to false if you don't want swapping to work in this case.
As an alternative if you do want swapping and instant swapping so the swapping doesn't have all the side effects of a graphics reset then you might just want to tone down the actual internal render resolution. You can do this with the 3D render size which will set the internal render size for all windows. This may result in scaling up or down for the actual display depending on the region. This option will work best if you know what the size of the main window will actually be so you can choose a 3D Render size with the same aspect ratio (to figure it out I create a Window Layout of the type I want first, check the resolutions, and then make a new layout with the new gained knowledge). In the corner layout the main region would be 3040x1280 so I can scale that down and keep the aspect ratio with a 3D render size of 1710x720. This would be a total of 9,849,600 pixels to render for 8 games.

If the 3D Render resolution was bumped down to 1520x640 which is a more sensible size being half scale then it is 7,782,400 pixels for the 8 games. So a little bit closer to the tiled layout total pixels, looks a little better on the bigger window, and still lets you have swapping when you need it. I'm not sure that the 2m pixels would make that much difference overall.