"It is a funnel, you look at the stages, and at the end there is a great engineer that is usually working for a long period for the company.
Each level has expenses and conversions. Go an optimize keeping in mind the constraints."
But what I noticed is that is all about your company specifics and how you overcome the trade off...
For example the average new startup in unsexy industry has problems to get any body in the funnel. Getting somebody that know how to write some code can be a challenge... interview is more about persuading them to accept the job.
Great "sexy" companies have ton of people applying and would do everything they ask them to do. The problem for the company is to efficiently select those people.
When you have enough candidates, somebody may think: "We can save time and make accurate evaluations by giving a screening test offline to evaluate most of the relevant skills of the person!". Unfortunately the test takes on average 10 hours to finish.
Result: mediocre candidates desperate for a job try so hard to get everything done, but the great engineer has plenty of options and does not want to spend 10h on a test. In the end all great people that you would like to hire quit in the process.