Over time, links get broken, data is incorrect, advise is outdated, etc.
If you had a sequence for the automotive market for example and one of your posts complained about $1.74 gas, people would think you were either crazy or they signed up to an old list.
If you were in the IM world and had a sequence post about Overture, then people would know pretty quickly your stuff is stale.
That reminds me. I need to go view my autoresponder.