Hi Venkat,
i think, below link will cleare your doubts. its impact query performance. to improve that we use line item dim.When dimnesion(size) occupy more than 20% fact table size.
http://scn.sap.com/people/juergen.noe/blog/2007/12/07/spot-on-line-item-dimensions
http://premkolipaka.blogspot.in/2012/05/line-item-dimension_7787.html
Line item impact:
http://scn.sap.com/thread/1373532
Sorry - load performance improvement is wrong one
Thanks
.