in my update statement, the condition is such that the column may get changed from 1 to 2 and next time when update happens that set of data with value '2' is going to get updated again.
batch approach always give leverage to handle the resources like memory , disk space and also we can schedule it for off-peak hours. and to handle your "adhoc updation hiccups" ,
1) you can set a update trigger so that you can catch the records which are being getting update during batch process
2) and save them in any temp table
3) once the batch got completed pick those values from that temp table and update the new column.
4) drop the temp table and trigger once the new column populated completely.
-------Bhuvnesh----------I work only to learn Sql Server...though my company pays me for getting their stuff done;-)