A few reasons:
- Stall manufacturers allow the possibility of approximately 1/4" variance on their specifications.
- If your shower door will be replacing an existing shower door it's possible there are existing stains and holes already for wall jambs. This means you may want to adjust where exactly you want the curb and wall jambs to sit versus the exact center line
- Headers are long as all walls are not perfectly plumb and headers will need to adjust to wall conditions to end up with level vertical posts.
- All extrusions for neo enclosures are aluminum and can be easily cut with a hacksaw and mitre box. Tip: using some form of cutting lubrication makes cutting it much easier
