When dealing with this type of information part of the answer will depend on what field of work you are dealing with. The tolerances for construction are not even in the same ball park as some one working with optics or computer circuitry.
Having said that I find personally try to draw as accurate as possible, but set visible dimensions to the degree of accuracy which is reasonable for what I am working on. This is also going to cause some grief at some point down the road where you will need to figure out with your experience what you will want to do or ask the designer how they want things to be displayed.
In my field a classic example of over dimensioning which is always done can be as follows:
The over all dimension is 9 mm. Dimensions are displayed to the nearest mm. You need to dimension to the mid point from both side for some reason (I did state this is classic over dimension in my field) You can easily draw the mid point in at 4.5 which is what you should do. When you go to subdivide the overall dimension you will either wind up with two dimension that show 4 or two that show 5 depending on how your system rounds. As a result, your subdimensions will not add up to your overall dimensions. You could cheat a bit and nudge the mid point 0.01 mm left or right and this would give you subdimension of 4 and 5 which add up correctly but does not position things truly in the middle. My field does not use the equal notation so if I am drafting for someone else I set the accuracy to 4.5 for those dimension then check with the designer when they review. If I am the designer and the drafter, I try to adjust the over all dimension to something that will subdivide nicely.
As Transistor stated in their answer. If you are sending it to a CNC machine A computer will just do whatever the numbers you supply it tell it to do until it finishes, or throws an error.
Below is how I would dimension and draw your 1200 sign. Not the alternate units [xx.xxx] is what is stored in the program and are shown for demonstration purposes only, I would not include them in a drawing.
This what I would wind up sending out on a hard copy.