What's the point of making a simple image in computer graphics? There are several, the first reason is technical, we can afford very high resolutions, about 20 to 40 Mp, which is almost impossible (for an individual in all cases) with animations.
Then we can go very far in the small aesthetic details that'll make your image will be beautiful rather than only nice, and it's even advisable to have an highly detailed picture! Because if your image is viewed on a single screen, not all the details will see, but if the same image is found printed in one meter wide, full details will be see, and you rarely know in advance what will be the end use of your images.
Last thing, in principle computing time are reasonable. On my PC, which has a six-core processor operating at 4 GHz and 32Gb main memory, my 30MP images are calculated between 15min and 6 hours each case to case.
The most critical cases being excessive use of materials such as chromium, gold, glass, ... Generally, any substance which has the reflection and refraction will be time-consuming calculations. Unfortunately for me, these are my favorite subjects!
An example is always much louder than words, here is a picture that took about 6 hours calculation for a resolution of 30MP. Why? Many complex reflections and refractions of different materials, and small detail called "caustics" (these are the reflections of white light you see on the ground), it's more realistic, but the computing time increases accordingly. Without these caustics, it removes almost one hour calculations!
The image in left for example, always in a 30MP resolution, took only forty minutes from calculations only.
Because the material is bright red, but that's all, it's not complicated to calculate for 3D software.
The same for the shadow, is also a basic element. Finally, the shape of this object is very simple compared to perfume bottles that have shapes much more complicated!
In summary, in the world of digital graphics, the more we want to produce images close to reality, or abstract images, but with lots of details, and more computing time will be important!