While “since” can be used to denote causation, using the word in such a manner can lead to confusion.
- Confusing: Since we won the contract, we drank
- Not confusing: Because we won the contract, we drank.
The first example might be ok if you are referring to the events of the previous evening. But what if the contract was awarded three years ago? A reader might think you’re on one hecukva bender.
To minimize ambiguity, avoid using “since” when you can use “because” instead.
Often writers use “since” as a conjunction as the first word in a sentence because they don’t think it’s ok to start a sentence with “because” (I was taught that rule in elementary school). There’s nothing wrong, however, with doing so.