Beginner SQL developers prefer NULLs, because it is the low maintenance overhead approach.

Expert database designers caution against using NULLABLE columns because they introduce 3-way logic into joins, and forces the frequent use of ISNULL function.

To avoid NULL usage:

1. Set default on each column such as 0, '', '01/01/1900'

2. If you have to know that column was populated or not, add a IsColumnX bit column with default 0. Update it to 1 when ColumnX gets populated