Altering column from INT to BIG INT and fill factor trick
I have to tell you the only answer I can come up with is "This makes no sense what-so-ever".  

From what I can tell they were expanding the table out so there was room for the additional space for the BIGINT.  They then dropped the primary key (presumably the clustered index as well) to avoid some of the time spent increasing the column width then re-created the primary key.

I've never tried this so I can't tell you how long it would take but I can tell you after a great deal of testing which way I went on a similar task.


Script and drop all indexes except the clustered index.
Create a temp table with the correct structure
Copy the data from the existing table to the temp table
Rename swap
Re-create required indexes 
Drop original table


I wrote about the logic of it in more detail here.