I would say that half of the receptions I shoot would eat a natural light shooter for lunch. To offer wedding services without being ready to handle these situations seems to be unwise, to put it mildly. Preferring to shoot natural light is a perfectly valid approach for wedding photography, but it really has to be paired with the knowledge of how to manufacture light when the light on scene is lacking in quantity and / or quality. To re-emphasize: this situation WILL occur.
In the majority of situations I do not use flash during a ceremony, shooting mainly at ISO 1600 and f/2.5 ish. For processionals I'm usually using the 50mm and like to be around 1/200.
However, if the clients, the venue allow the use of light and I feel like it's feasible to introduce (low enough ceilings, a place to put speedlights that isn't too intrusive) and will be required to deliver the results my clients expect of me, I'll use it. I'm probably using flash at 30% of the ceremonies I shoot.