Hello! I would like to suggest adding a feature that I think would be very useful and greatly simplify life for many users.
Add the ability to place a wall or object at a precise distance from another wall, using either numerical input or snapping to dimension lines. This will significantly improve the accuracy of interior planning, especially when working with interior partitions. Thank you!

You can already do that. Select the wall you want to move and select the function Modify walls (Ctrl+Shift+E). You can set the exact position with the X and Y coordinates of the start and end points of the wall.
Want a new wall parallel to an existing wall but 500cm to the right? Copy the existing wall and unselect it. Now past the new wall, it will be at the exact same position. Press Ctrl+Shift+E for the Modify walls dialog and add +500 to the existing X coordinates. It will calculate the new X coordinates. Do the same with the Y coordinates if you want to move a wall up or down in the 2D view. You can also change the wall lenght: it will exend along the wall direction.
Almost every numeric field in Sweet Home 3D is a small calculator that can handle complex mathematical formulas, including the use of parentheses, i.e. ((22*2)+(12/2))/3. Use it!

Positioning along dimension lines is not possible. Usually these are added after placing the walls.