Cost and Labour Advantages

 No scaffolding or safety netting in most situations.
Roof lifted and frames fitted in one day. 
Work can start immediately on the interior. 
No need for soffit dwangs/nogs. 
 Additions/alterations to window/door openings can be made anywhere in the exterior walls.
Less chance of damage to trusses and roofing material. 
 Improved quality of work.