Marketing user checkbox in Salesforce is used for the following:

– To create a new campaign record
– To edit an existing campaign record
– To delete an existing campaign record
– To modify/change/update campaign statistics
– To Import Lead records into a Campaign(CampaignMember entity)*
– To mass/bulk update the status for Members of a Campaign*
– To configure advanced campaign setup to define member status values
– To run Campaign reports across multiple Campaigns

* In order to use the campaign Import wizard, Marketing Users must also have the Marketing User profile (or the “Import Leads” Profile permission in Enterprise Edition organizations).