Need a clarification - (Jun/17/2014 )

Why do you have to passage a cell line? Why not use it as it is?

I'm not entirely sure of the question - use it as is?  How do you think it got to where it is?

In short: because if you didn't passage cells, they would grow more and more confluent, and over time nutrients from the medium are consumed, until there is not enough nutrients left, and the cells would die.