A campaign with import rules may accumulate massive lists of keywords over time.
Having tons of keywords in the same ad can have some undesirable impacts:
The campaign budget may not be sufficient to drive traffic to all the keywords.
High-volume keywords can take traffic away from low-volume keywords, resulting in missed opportunities.
It takes longer to optimize ads because only a subset of keywords get traffic.
It becomes harder to split the advertising budget between keywords.
X-keywords per campaign structure
You can reduce the problem by creating multiple campaigns with a limited number of keywords (Etc. 10 keywords per campaign).
Such a structure gives more control but means more work, as you now have to do the following:
Aggregate and analyze search terms across all the campaigns.
Identify good search terms, and find if the keywords exist in any campaigns.
Add keywords to an existing campaign, or create additional campaigns to hold these new keywords.
Set up automation for these new campaigns.
N-tier campaign graduation funnel
A more automated approach is a performance-based graduation funnel.
Set up structures where keywords graduate progressively from one campaign structure to another based on performance.
For example, Mass Campaign > Fully Managed Campaign uses such a structure.
The Discovery campaign imports search terms with >= 2 orders.
The Sales campaign imports search terms with >= 5 orders and >= 15% conversion.
If you drive a significant traffic volume, consider creating even more campaigns with increasingly stringent criteria to funnel keywords into their campaign performance group and negating graduated keywords from lower-tier campaigns.
This graduation and negation approach reduces competing keywords and the number of "effective" keywords in each campaign.
You can automate the graduation and negation process for the N-tier funnel by referring to the Discovery and Sales strategic objective.
While X-keywords per campaign structure gives more granularity and control, N-tier campaign graduation funnel is helpful if the eventual goal is to uncover potentially rankable keywords to create a single keyword campaign structure for them.