There's few threads that are recent about how to set this up.
IF you want to be able to view photos, these must be synced.
If you do not care, you do not need to sync at all.
In the Setup->Computer menu on TV, select if you want to sync anything at all by selecting the top choice. You can then sync and stream. In iTunes, you'll have to uncheck the "show only synced content" box on the tv setup screen.
If you don't want to sync anything at all, then select the second option for a streaming computer.