While what you say is true for a short to normal Z travel, when the rails are on the front Z moving plate there are a couple major benefits:

- the overhang of is considerably smaller, like 5cm or more
- the rails themselves strengthen the plate
- the whole spindle body strengthens the plate if clamped with 2 clamps at all extension length
- once you have the design for 200mm you can easily change it for 300 or more mm Z travel