With “Instant Ship” campaigns, whenever a single order is placed, that order is printed and shipped to the customer, without waiting until the campaign ends.
With all campaigns, a human being checks your artwork to make sure there won’t be any problems printing your orders. In normal campaigns, your campaign goes live as soon as you launch it, before it’s checked. With Instant Ship campaigns, your campaign page will be available as soon as you launch it, but it will not accept orders until after your artwork is checked and approved.
Because each order is printed and shipped individually, your campaign does not have to reach its goal. There is no “tipping point” at which your campaign becomes successful. All orders are printed and shipped shortly after being placed.
“Normal” campaigns allow you take advantage of bulk quantity discounts when you sell a large number of shirts that can be screen printed. But in order to print and ship each shirt individually, each shirt is treated as a one-piece order, and therefore costs much more to produce.
When you know you are going to have only a small number of orders.
When your design is a full-color design that would have to be digitally printed anyway (this makes the cost difference less).
When your design has a limited number of colors (so it can be screen printed) and you expect to sell a large number of shirts.