Recently, Dennis Treubig posted an article "ranting" about why he hates the straight leg raise as an exercise on The Manual Therapist (his use of rant). He makes some excellent points about about how it is a significantly inadequate intensity for quad strengthening and the fact that it is more of a hip exercise anyway. He also states that it is useful for special testing and assessing neuromuscular control in patients with LBP.
While I may agree with those points, I do not think the exercise should be disregarded altogether. For one, the exercise is functional. If you think about segmental rolling leading with the lower extremity, this is an activity many people do in order to get out of bed each morning. Secondly, I think the exercise is essential for motor control training, not just assessment. When you monitor a patient's pelvic and lumbar position during any open-kinetic chain hip flexion, you may notice anterior pelvic tilt and/or lumbar extension, especially if the patient has back pain. Being able to progressively load hip with open-kinetic chain flexion can be useful for improving lumbopelvic motor control and stabilization. We should be able to flex the hip without excessive mobility occurring in the lumbar spine.
I don't want to brush Dennis' rant off as inaccurate, because he definitely makes some excellent points. In no way should we be using the SLR as a strengthening exercise for quadriceps. Additionally, as PT's we need to do a better job prescribing the appropriate dosage for strengthening exercises in general. However, I do think the SLR has some usage as an exercise still for motor control and functional training.