Right now Liquid it's only available inside templates and emails only, but we are missing some functionality by not having it available inside journeys.
Use case: opt-in form with First name and Email.
Problem: some users fill the form with their full name, making it an issue to use that variable when personalizing email
Solution: use Liquid within Journeys to format that value into a separate custom field.
Here's a perfect example of that working within an Automation with ConvertKit: https://mattolpinski.com/articles/convertkit-subscriber-names/
Basically, we can trigger the journey for every new subscriber, or we can do manually by applying a tag to them. This forces them through the migration (useful for past subscribers).