Yes, there are benefits that suit many shooters. By decoupling the AF function from the shutter, and setting the mode to AF-C, you have complete control of focusing for both moving and static subjects and recomposing without starting the focusing process. If shooting a static subject, press the AF-on for the exact focus point needed, such as an eye in a portrait. The most sensitive and accurate focus point is the center cross point. When focus is achieved, release the AF-on button and recompose as you wish, for rule of 3rds or other preference. If the subject has not moved forward or back, focus will still be good, discounting any field curvature. Without any setting change, if the subject moves, AF-C continuous focus tracking is engaged as long as you hold the AF-On button. Both static and active subjects are shot with the AF-C mode. The only disadvantage is AF-C mode does not enable the AF Assist light that is needed at times shooting in very dark conditions. The newer cameras such as the D7100, D600, D800 and D4 are all very good in low light focusing however. There is no need to stabilize the VR by the 1/2 shutter press. I had run tests to see if there is a difference in performance by allowing the system the fraction of a second that a a 1/2 press provides and found that any full shutter release is enough time to settle into the stabilized image. That makes logical sense since the response time of the driven element is so fast that it reacts to minute and fast camera movement due to shake in less time than the 50-60 ms shutter response.
Recomposing means re-metering so having the AE-L function available gives you total control of focus(af-on) and metering(ae-l) without any adjustments or removing your eye from the VF. Locking metering is needed because even in Matrix meter mode that considered the entire scene, it is still biased toward the level under the current focus point so you have the choice of metering on the subject you focused on or another tone level in the scene. It sounds complicated but after short practice it is almost automatic how you determine metering and focus independently from the shutter release. It gives you much more control of how the image looks when captured. Stan St Petersburg Russia