What happens if you leave it
Condensation tide-lines
Internal glass picks up faint mineral lines from condensation. They only really show in low winter light — but they're there year-round.
Dust on the top edge
The top inch of every internal pane collects dust that never gets wiped because nobody can see it day-to-day. It shows on photos and viewings instantly.
Streaks from kitchen spray
All-purpose kitchen sprays leave a film that smears in sunlight. The more you wipe, the worse it gets.
Marks from pets, kids and cooking
Nose prints, finger marks, splatter from the hob and steam off the kettle build up gradually and dull the whole room.