The uses for the Modern Language Aptitude Test include selection, placement and diagnosis of learning abilities.
Selection. The MLAT can be used to select individuals who show promise in learning foreign languages in order to justify the time and expense of placing them in a language training program.
Placement. In situations where there is more than one class or group of students in a language training program or course, the students can be placed according to their language learning aptitude so that each class can work at the most beneficial pace.
Diagnosis of Learning Abilities. The MLAT can also be used in conjunction with other forms of evidence to diagnose a foreign language learning disability. Looking at an individual's score on the different parts of the test can be help to match students' learning styles with instructional approaches.
Security. Because the MLAT is sometimes used for high stakes purposes, test security is tight. As a result, in recent years some researchers have used the LLAMA Tests, which attempt to test the same abilities, but use item types quite different from those used on the MLAT.
If you are going to sit the Modern Language Aptitude Test or would like to try your hand at the test, you can access over 600 questions here.