When you need to see the original events: In most cases, summary indexes are used to store aggregate values. A summary index could be used to store a separate copy of events but this is not usually the case. The more events you have in your summary index, the less advantage it has over the original index.

When the possible number of categories of data is huge: For example, if you want to know the top IP addresses seen per day, it may be tempting to simply capture a count of every IP address seen. This can still be a huge amount of data, and may not save you a lot of search time, if any. Likewise, simply storing the top 10 addresses per slice of time may not give an accurate picture over a long period of time. We will discuss this scenario under the Calculating top for a large time frame section.

When it is impractical to slice the data across sufficient...