George Michie has a must-read post over at SEL on the all-too-real perils of over-relying on automation to generate paid search keyword lists.
Not infrequently, we've seen such "tools" produce dangerously off-topic, ineffective and costly advertising.
From George's post:
While a controlled use of tools is valuable to build out and maintain the long tail, there is no substitute for human understanding in the more general, higher traffic category and subcategory terms.
Machines leave gaping holes and invariably use synonyms that are completely inappropriate - think about that "costume jewelry" category.
Cleaning this dangerous stuff out of a massive list takes more time that building the list carefully in the first place through machine assisted but human driven processes.
Full SEL article: Don't Let Machines Write Your Keyword List