Doors don't technically need architrave as it doesn't serve any structural purpose. It is purely for decorative. However, if you don’t use architrave you will usually notice an unfinished, unattractive look around your doors where the casing meets the edge of the rough opening. As well as covering uneven edges, the architrave can act as a protector for the edge of your walls and prevents damage to the plaster. If it’s left off, then these edges can start to flake or chip which even further damages the look of the doorway.