Does anyone know whether there is some advantage to doing a separate campaign instead of a separate adgroup, or vice versa? It seems to me just from observation that Google places a new campaign more than a new adgroup (but it could have just been those particular topics)and I am looking for robust placement as I try to convert tens of thousands of customers per month from AdWords. I know there are probably a lot of variables but if anyone has insight I would appreciate it. An example would be if I were advertising on two different currencies (for investment) to convert people to the same product. Also to consider, the campaign I am thinking of adding an ad group to is one of my top performers and Google puts it all over the place. I don't know if that would have an effect, making it more advantageous to do an ad group in a well-performing campaign than to do a new campaign.
The advantage of a separate campaign for a new adgroup is that you can control your ad extensions on a more granular level. The advantage (albeit only a small one in the grand scheme of things) of starting up a new adgroup is that you gain the benefits of the prior campaign history.
If the differences between the new adgroup and previous ones are minor enough that you don't need to play around with new ad extensions, you probably don't need a new campaign.