Say you have a nice blueprint for rails. You put it in 50 locations already and want to add some lights now. Why do it manually if you could change it in blueprint and see it instantly applied as ghosts everywhere. Same with upgrades, dismantling and redesign. There should be a mode to place a blueprint that you expect to modify later.
Why?
Why changing manual placing to automation is good is probably a strange question in Factorio, so I would rather write why it may be bad and how problems may be addressed.
- Game have to implement blueprint editor
- Game have to keep track if something is part of a blueprint or a "raw" buildings
- When you modify blueprint new stuff may collide with something.
- It may collide with matching entities
- When you dismantle part of blueprint you don't want it to be rebuilt instantly.
As for colliding with other stuff - couple buttons like "absorb" and "force" in blueprint editor should be enough to solve most of the issues. And blueprint editor should probably show total amount of unresolved collisions.