"Targeting criteria applied to a campaign"
That is Google's definition of utm_marketing_tactic, and its two examples are remarketing and prospecting. Remarketing shows ads to people who have already visited a site. Prospecting reaches people who have not. The tag records which of the two an ad was doing. Either a marketer or the ad platform sets it.
What Google says about reporting
Google's UTM help page lists the parameter with a note: "utm_marketing_tactic isn't currently reported in Google Analytics properties." Its sibling utm_creative_format carries the same note, yet GA4's dimensions reference does list manual creative format dimensions for that one. For utm_marketing_tactic, the same reference listed no matching dimension when we checked it on September 27, 2026. For now the tag rides on the link and standard GA4 reports do not show it.
The mix-up with utm_medium
utm_medium is the field GA4 does report. Google describes it as the marketing medium, with cpc, banner and email as examples. That is the channel. utm_marketing_tactic is the audience approach inside the channel, so a remarketing ad and a prospecting ad can both be cpc. Writing remarketing into utm_medium to force it into reports puts a value in the field GA4's channel grouping reads, and the visit can land in the wrong channel.
If you need the split in reports today
Leave the tag in place if your ad platform adds it, since it costs nothing. If you need remarketing and prospecting visible now, put the difference in a field GA4 reports, such as the campaign name in utm_campaign. A visitor can delete it from a link without any effect on the page, and it holds an audience type, never anything about them.