It is a good plan to structure your AdWords account using themes with a different theme or service in each ad group, but make sure that when you are structuring your account that you plan to grow in an effective way.
I have seen in the last couple of weeks a few accounts that simply got carried away with the idea of creating new ad groups. One account had over 20 ad groups with several competing between themselves, another account did not group products together and had 50 ad groups with some that had only one or two keywords in the ad group. Another I reviews, had so many campaigns that the budget for some campaigns was so ridiculously low that it was no wonder that they had no impressions for the entire month.
If you self manage your AdWords account, you have the opportunity to create as many ad groups as you want, but when you have 15 to 20 ad groups and you want a professional such as myself to manage the program for you, you will pay your account manager to open each ad group and manage each program. It typically takes us three hours of our time per month to work on a program with 10 ad groups and that is on a once a week schedule. That’s after the account is really performing. If you have a program that is not performing, double that time for management – that’s six hours. You can just get carried away creating ad groups that you really don’t need that will bloat your account, parse your budget too many ways, and compete against each other.
When we create ad groups we definitely want themes, but also keep an eye on the budget and the time it will take to manage your program. We want your full AdWords program including management to be an investment in your success not to be an expense.