>In a table having about 26 million records and counting, it contains only a few fields however, what would be the impact of using Char(100) field VS Text or NVarChar field, whatever the field type which would be used? The reason I ask is that the first 26 million records won't have a value in this new field. It is just a caption to enter some text about upcoming images. The table takes 30 GB presently totalling the data + index + reserved. Whichever field type I choose, would there be a space advantage of one over the other or this doesn't matter in SQL Server?

with 26 Miliion record with null value the better solution is
VARCHAR(100) with Sparse attribute