Hi Slava,
Thanks for using Syncfusion products.
The AllowProportionalColumnSizing property is used to adjust the column’s width of the grid to fit the total width of the form or where the grid is placed. If resize the any of the column by using mouse, the width of other columns will be adjusted to fit the total width of form.
The ResizeToFit property is used to fit the column width based on its content width. If both AllowProportionalColumnSizing and ResizeToFit are used in the sample, AllowProportionalColumnSizing will be enabled and grid size will be changed to fit the Form (column widths will be equally adjusted to fit in the parent form).
Please let us know if we misunderstood anything.
Regards,
Piruthiviraj