Text Length Override is a Field User Property and is used to restrict the text entered in a column.Now suppose the requirement/ business rule is that the column should not allow the text greater than 30 char and all the columns which are present on the DB for reuse is of length greater than 30 say 100,250, etc.
The first option a developer is look for will be creating a new column but here we have restriction that we cannot extend the column.
There are many empty columns on the DB for re-use then we can use this property to restrict user to enter the characters to desired length (less than the max length of column used ) no matter the size of column used.
Now if we directly give this column in field then user will be able to enter 100, 250 char etc but that is not required therefore in the field which uses the column of length > 30 char we add a field user property “Text Length Override” and leave the Value column null.
While creating a field the text length property decides how much character a user can enter in the fied. So if the column on the DB level has 100 char and in the field the text length property has 30 as value the the filed will accept 30 char only and not 100.