If you are sitting in the middle between your speakers, and the speakers aren't total garbage, then there is no reason to add in a center channel.
What is it doing for you? Dialog will already be anchored dead center for you.
If you have a bunch of off access viewers, then yes, a center channel would be good to anchor the dialog.
This is more a question for you. Do you care about surround? If so, go 4.0 and add in the surrounds. If not, go 2.0. If you sit off access, add in the center. If you like bass and want impact, add in a sub
What is it doing for you? Dialog will already be anchored dead center for you.
If you have a bunch of off access viewers, then yes, a center channel would be good to anchor the dialog.
This is more a question for you. Do you care about surround? If so, go 4.0 and add in the surrounds. If not, go 2.0. If you sit off access, add in the center. If you like bass and want impact, add in a sub