'Hide Header' can be used in situations where it is advantageous to remove your main website menu navigation.

PRO TIP:

The most frequent scenario is for 'Landing Pages', that focus on Conversion Rate Optimisation (CRO). 

Often removing a header improves conversions rates for marketing campaigns. The hypothesis is that users presented with fewer options/distractions are more likely to take your desired action.

E.g. if there is only the option to complete a form on a page (and no other links), the user is more likely to do complete the form.

Give this a try on you next campaign and track the degree to which your conversion rates imporve.