What are keyword limits?
By default, all campaigns in an account share the same common pool of keyword credits on a first-come-first-served basis. In this way, it's possible for a single campaign to use the majority or all of the credits in the account.
Keyword Limits allow you to allocate a portion of keyword credits for an individual campaign. When keyword limits are added to a campaign, it reserves these credits so they cannot be used by other campaigns. In this way, keyword credits used by this campaign are equal to the keyword limits set (regardless of actual keyword credits used), essentially reserving them for this campaign's use only.
Why might keyword limits be useful?
The use of keyword limits are optional, and is typically most useful for larger or independent teams. For example, if an organization has multiple teams or offices, each working independently on their own campaign, keyword limits can help make sure one team or office doesn't use more than their fair share of keyword credits before other teams have a chance.
Example in action
Let's look at a sample account with 3 campaigns:
Campaigns A and C have keywords limits in place of 500 and 450 respectively. Therefore, even though they are only using 300 and 0 credits currently, 950 credits are utilized by these two campaigns.
Campaign B has no keyword limits applied, so utilization is based on the actual usage of 200 credits.
The total current credit utilization is therefore 1,150.
Assuming that there are 2,500 total credits in the account, this would leave 1,350 available.
Campaign A, with a limit of 500 would only be able to use up to 500 credits.
Campaign C, with a limit of 450 would only be able to use up to 450 credits.
Campaign B, with no limits in place would be able to take from the shared pool of up to 1,350 credits.
Since Campaign C is allocated limits of 450 but is using 0, these credits are reserved but unused.
If the limits of Campaign C were removed, the number of available credits would increase from 1,350 to 1,750.
In this new arrangement, Campaign A would still be limited to 500 credits, but Campaigns B and C would be able to use up to 1,750 together. Any credits utilized by one campaign would be unavailable to be used by the other.