How does just-in-time processing differ from the conventional manufacturing process?

Just-in-time processing differs from conventional
strategies in that it tries to ensure that a company has as little inventory as
possible.  The reason for this is that keeping inventory around incurs costs, generally
called carrying costs.  Therefore, a company that is able to manage its inventory on a
just-in-time basis can save money.

In conventional
strategies, companies keep excess inventory around on what is sometimes called a
"just-in-case" basis.  They want to be sure that they are never caught not having an
item in inventory because that would mean that they might lose a
customer.

Just-in-time inventory management is meant to
keep customers satisfied, but without having the costs of keeping inventory around. 
This means that a firm must keep very careful track of how much inventory it has and how
much it is likely to need.  It then orders the exact amount of inventory it will need
and it times its orders to be sure that it will only receive the inventory right when it
needs it.

Just-in-time is a much riskier strategy.  It
forces a firm to be very accurate in its forecasting of what it will need and when. 
When it works, though, it is a very good way for a company to save
money.