Founders should stay involved in the business questions — where to expand, how much risk to take on a new channel, what the company can't compromise on — but should hand over the day-to-day marketing decisions entirely. A fractional CMO who's second-guessed on execution details can't actually operate as a strategic leader.
A useful test: if the founder is approving individual ad creative or email subject lines, the fractional CMO relationship isn't set up to work yet.