The difference between using extract during in your search and setting up search time extraction is with search time extraction, the fields are available for using without having to extract them every time. Also allows you to create aliases etc. With the extract command, you will have to repeat the extraction with every search.
To enable to search time extraction, you will need to make the following changes
*Transforms*
[kv_pair_delim]
DELIMS = ",", "="
*Props*
[your sourcetype stanza]
REPORT-activity = kv_pair_delim
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