This feature is a 'magic' button that modifies column width and row height based on contents, to optimize PowerPoint table size. The feature autofits to create the smallest height table possible (given your table's content).

PPT Productivity's PowerPoint Autofit columns feature keeps the width of your table but adjusts each column's width within it based on the contents. Use this feature once you have finished entering data into your table.

Note - the autofit column feature was updated in May 2022 to make the feature faster and to prevent longer words breaking within a column.