Greater tier points
Greater Avios
Empty middle seat/more personal space/more private/less crowded
Priority disembarkation
More personalised service
Enhanced catering including proper meals at breakfast/lunch/dinner
Enhanced drinks service including champagne
'Exclusivity' factor
Reduced ChavChance

And if one doesn't have status:

Priority check-in
Increased baggage allowance
Fast Track security
Lounge access
Fast Track boarding

The 'only' difference between convertible and non-convertible seating is the width of the seat being less for non-convertible seating. I don't find this acceptable, but it's only one component of the CE service.