Bishoping a province is a great strategy that has it's place. You have to know when to use it.
The ideal situation is you get your deck down to Bishop/Province/3 treasures that add to $7. Every turn you bishop the province and buy a new one. The key component is how fast you can get the game to this state.
The strategy functions a bit like a turbo-remodel strategy (where you'd remodel your own provinces into provinces just to end the game quickly).
You are essentially gaining 5 points per turn, every single turn, while 100% guaranteeing that you gain 5 VP every turn afterwards, while accelerating the end of the game.
When to use this strategy:
In a province game, and
When you see the opponent open with a slow buy such as a potion, and
When there is a strong trasher (i.e. Chapel, Steward).
Straight-up bishops will trash this deck down, but will usually do it too slowly.
So say the board is something like Steward, Bishop, Loan (for example).
I would open Steward/Loan, trash my deck down. As soon as I can get $6, buy a gold (usually with steward) then Bishop right after. Then Clean my deck down to Bishop/Gold/Silver/Silver/Province as soon as I've bought my first province. Then I'm off to the races.
You put your opponent on a really quick clock with this strategy. The key is a fast trasher though. Don't try this just on bishop trashing alone. You'll end up speeding up your opponent just as quickly as you, but he'll likely win the race even going something like BM + support (with your trashing helping him).