Here is a use-case of customer metafields. Some vendors wants to add customer numbers and account managers attached to each customer’s information/profile and display additional information on product page based on this specific data.

{% if customer %}
    {% for metafield in customer.metafields.Namespace%}
        {{ metafield | last}}
    {% endfor %}
{% endif %}

Above code will loop through the customer metafields which share a common Namespace and prints out the value of keys

And by using if or switch statements you display additional data.

{% if customer %}
    {% for metafield in customer.metafields.%}
       {% if metafield.last == 'gluten allergy' %} This product is gluten free! {%endif%}
    {% endfor %}
{% endif %}