From the Magic Lantern User Guide #Features, here is a sample of features that apply to photography:

• Exposure helpers: zebras, false color, histogram, waveform, spotmeter, vectorscope.
• LiveView adjustments: contrast, saturation, display gain for using LiveView in darkness.
• Cropmark images: user-editable overlays to assist framing and composition.
• Fine control for ISO, Shutter, Kelvin white balance and other image settings.
• Bracketing: advanced exposure bracketing, focus stacking.
• Timelapse: intervalometer (for photos and movies), bulb ramping (manual and automatic), recording at very low FPS (down to 0.2 FPS), silent pictures without shutter actuation.
• Astro- and night photography: bulb timer for very long exposures (up to 8h).
• Info displays: focus and DOF info, CMOS temperature, shutter count, clock.
• For strobists: flash exposure compensation, range up to -10 to +3 EV (depends on the camera).

I think it is self explanatory that having features such as those listed above is beneficial. Would I like to have a built in intervalometer, of course! Would I like to have further control over bracketing, of course!

It allows you additional fine tuning and control that you either would need additional hardware to achieve, or simply is not possible without extra manual steps.

If you have a camera that is compatible with it, I see very little reason why not to install it and keep it installed. The additional functionality and essentially free added features are welcomed to me.