By default, yes, but you can prevent it.
I'm away from my computer at the moment, but if memory serves you can turn off just the backup on the Summary screen in iTunes, or at least switch to iCloud . That will leave the auto sync in place but skip the backup.
You can also disable auto sync for individual devices Unless you turned it off in preferences as I described in the earlier post, then it is grayed out.
I prefer to turn all the auto-stuff off and do it manually. I often launch iTunes and/or connect my devices several times a day; fact checking for forum posts mostly. I don't need to do syncs or backup that much.