There are many advantages to in-line test processes. Speed and coverage would probably, in my opinion, be the largest advantages. You can inspect more in less time with an automated test/inspection system. When using off-line inspection you often have to implement a sampling plan or choose which parts you will or will not inspect and with in-line you can get all the data.

Many times the in-line versus off-line conversation also leads to the 2D versus 3D debate. So, when evaluating an in-line versus off-line system you need to look at coverage and capability too. You will want to match that up with what you are trying to accomplish.

In-line tests help prevent using manufacturing capacity on a production line to build a product that is already defective. It identifies the problem and then a human can make an informed decision whether to throw out the defective product, send it over to rework right then, or send it through the line as defective, with it marked for rework as soon as it comes off the line.

The key goal is knowing that you have a defect, it does not get out the door and you maximize yield and manufacturing capacity. This also identifies if you have a large number of defects identified that something needs to be fixed on the line prior to that test point.