Say I register XYZ LLC, And the business will be conducted under XYZ.com Do I need a DBA for this? I could mention the site in ad copies without the LLC suffix?
Depends, are you going to sell in your state? If so then it is a must, if not then don't worry about it.
If you aren't selling then you aren't selling. If you are selling then you need a DBA. (In other words, if you have a buy now button you need a DBA, unless the website is your *first & last name.com*
State rules vary. For example, if you XYZ LLC obtains a trademark registration for xyz.com, in many states you can operate the business under a trademark with also registering the DBA. In most states, registering an assumed name (DBA) for an LLC is easy and inexpensive. When in doubt, I would suggest that you register. Contrary to what Ferrari310 wrote, I don't know of any state where "selling" something is directly relevant to the determination of whether you need to obtain an assumed name, unless he/she is simply using the term "selling" as a substitute for "conducting business". If you run ads on the site, you are conducting business, whether you call that "selling" or collecting commissions or PPC revenues.