I inherited a Google Adwords account with about 65,000 keywords.
Today while scrubbing the account I happened to click on the home tab where I got the following alert.
Here is the text verbatim:
The keywords in your account are nearing an unmanageable size. We recommend that you reduce the number of keywords within your account. This will ensure that your account includes the most targeted and relevant keywords possible.
Use our Adwords Editor to identify poor performing keywords within your account (such as keywords with few or zero impressions) and delete them.
Note: Be careful when deleting keywords in campaigns that are only opted in to the Display Network. Impressions and other statistics aren’t attributed to individual keywords when ads show on Display Network pages, but are attributed to the ad group as a whole. Therefore, keywords in Display Network-only campaigns will always show zero impressions.
The “Note” portion of the warning kind of complicates matters doesn’t it?