For some types of websites, this might be super useful, but we find our strings are usually stored in the format in which we want to output them. And for numbers floatformat is generally more useful.

One case where stringformat can be useful: comparing a value on the querystring, which is always a string, with an integer property of an object (e.g., an id). For example:

<select name="user" id="user" class="form-select">
  <option value="">User</option>
  {% for user in users %}
    <option value="{{ user.id }}"{% if request.GET.user == user.id|stringformat:"i" %} selected{% endif %}>{{ user.full_name }}</option>
  {% endfor %}
</select>

Thanks to Simeon Visser for this Stack Overflow answer.