Artists hold a color pencil as close to the tip as possible to draw detail. The same goes for an airbrush as the outlandishly talented Alberto Ponno indicated. In the design of many airbrushes this is an underrated construction feature. In side cup or siphon feed airbrushes and gravity feed (with the paint cup placed on top) airbrushes the distance between tip and trigger are different which is inherent to their construction.
In the image below from top to bottom you see the Iwata Custom Micron SB, the Custom Micron C and the HP-BH. The vertical red line is a reference to distinguish the trigger position of the airbrushes which tips are aligned in one plane.
It immediately becomes visible that the gravity feed CM C has the greatest distance between tip and trigger (indicated by the blue line) and that the HP-BH has about the same distance as the SB. The Microns due to their internal construction have an advantage over any other airbrush where the spraying of fine detail is concerned. The HP-BH's smaller paint cup allowed Iwata to reduce the distance between tip and trigger, the bigger cup of the C forced them to place the trigger further away from the tip to prevent it from interfering with the artist's index finger.
Side cups of siphon feed are said to have a slower response than gravity feed airbrushes, because gravity does not assist in the flow direction of the paint - from cup to nozzle. In practice this slight delay is negligible; the jet of air and paint needs to stabilize in all airbrushes regardless of their construction. Gravity feed cup are always in the same angle relative to the airbrush longitudinal axis while siphon feed cups can be rotated in any desired angle.
The argument that gravity feed paint cups block the view is a fable. The airbrush is never used in a plane perpendicular to the midpoint between the eyes, but always in either the right or left hand to the side or off-center so to speak. When paint residue (tip dry) needs to be removed from a needle between paint refills, a siphon feed airbrush will not leak paint, where gravity feed airbrushes will. To prevent this in gravity feed models the artist can place his or her thumb on top of the paint cup to prevent paint from leaking, but this is only possible with small paint cups.
In the case of the SB the side cup can be inserted to the right or left, which makes the gun suited for both left and right handers. It may be a beneficial argument when the airbrush is sold as an occasion. These are the reasons why I prefer siphon feed airbrushes over gravity feed models - the shorter distance between tip and trigger, the possibility to rotate the paint cup in any angle and place it on the left or right side of the airbrush and the fact that they can be cleaned without spilling paint between refills.