If you were to play a 2.4 movie on a 16:9 screen you would do nothing to your projector. You would have black bars at the top and bottom of your screen. If you zoomed this to get rid of the top/bottom black bars the left and right portions of the picture would be off the screen.
Using the zoom or an anamorphic lens is used when you have a 2.4 screen. The projector is zoomed in so that the black bars are not seen as the are actually projected onto the black velvet frame. When watching 16:9 material on a 2.4 screen the projector is zoomed out and you will have black bars on the side.
Whether using a 16:9 or 2.4 screen, each has its tradeoffs depending on the material you are watching. An A-len is a better solution if doing a 2.4 screen, the zoom method is a poor man's method of doing a 2.4 screen but if you are a big movies buff it is worth it.
Since you plan on a 16:9 screen I wouldn't pick a projector based on a lens memory feature because you would never use it. Look at what other attributes best fit your needs.