This feature is designed to improve the experience for users when working with and designing HTML templates. The change allows users to create table columns that can be resized. The change was implemented to address customer requests specifically in email templates and now customers are able to control exactly the width of each column and the layout of the generated table.
Although implemented specifically for Email templates the ability to change and control the width of table columns applies to all HTML editors including document tables.
This allows users to layout emails and HTML documents in the way they want and improve the layout of information in a tabular format in emails and documents.