Used to vs would

We use used to/would to describe habits and repeated actions which took place over a period of time in the past.
Used to
-To describe extended past states we can only use used to
There used to be a church here.
I used to have an old car.
-To talk about regular and important habitual behaviour.
I used to smoke.
Maria used to go to ballet lessons 

Would is generally used when the time or topic are clear, otherwise the meaning of this modal verb wouldn't be clear.

(one customer to another customer in a shop)
I would buy that, but it's a waste of money.
I used to buy that, but it's a waste of money.