With many (if not most) reputable dedicated server providers nowadays Inbound traffic is not calculated towards your overall traffic. In other words, it's free and generally unlimited.
Remember that most loads are 1:10 inbound:outbound, so unless you have a strange sort of workload it really doesn't help you much.
If you do happen to have a lot of inbound traffic though, it's a nice little arrangement as the bandwidth may be almost free to the provider (Symetricity requirements) and still very useful to you.
I did not know that. My provider counts inbound which sucks because that's most of our traffic but we run at about 6 out of 10 terabytes per server per month so it's not a problem... for now.
If you do happen to have a lot of inbound traffic though, it's a nice little arrangement as the bandwidth may be almost free to the provider (Symetricity requirements) and still very useful to you.