SQL Server Table keeps big after schema change
Your rows fit in page, even with 100 spaces in Comments. Updating the Comments to ltrim(rtrim)) will make absolutely no difference in space used, since the rows will be left in place in their respective pages (ie. absolutely no page gets freed, you just get more space available on each page). To reclaim the lost space you should rebuild the table:

ALTER TABLE ... REBUILD;


Not that 3.7Gb is big by any stretch...