You can’t really hire someone based on an interview. Some people are good talkers, but bad workers or vice versa. Talk is cheap, and I really don’t want to hear how well someone talks unless they are going to do call center work. You can test prospective employees out on various projects — that is a good idea. But, what about a training program?
Most people are below standard in what you want to hire them to do. Selecting the best of a pool of below standard people might not be an ideal solution for your company’s hiring needs. It might make sense to put them through some training, and then evaluate them.
Additionally, having a training program allows you to see if people stick with you when you are being demanding on them. It also lets you see if they are capable of taking instruction or learning. Third, you can see if they have a bad attitude before you hire them. Ability is only one metric in hiring people, these other metrics are equally important.
Large companies often spend tremendous amounts of money on analysts to assess the value of their employees. You need to know how good someone is, so you know exactly how much salary to offer them. You can’t really tell that if you just hire them on some basic preliminary tests. Knowing how they learn and if they stick around gives you more data to assess their value to your company.