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Values of 2, 5, 100 ("Max final density" parameter was kept at 35 for all renders)
Min final density
The minium density in a particular cell of the volumetric object. In most cases you should leave this value at 0 as you don't want any
Max final density
The max allowable density in a particular cell of the volumetric object. Note that this parameter is also influenced by the Density Multiplier - a small density multiplier will not make the volumetric look more dense, even if the Max final density is very large. In fact, you should avoid setting this setting very high (for example more than a few hundred), especially if the density multiplier value is small. This will result in a similar look as if a smaller max final density value was used, with the downside that the render time will be substantially slower. As you can see in the example renders below, if the Density multiplier is already fairly large, then a Max final density value of around 100 will be enough even for the most "solid" volumetric simulations.
Cell size
The cell size should be considered as the "resolution" of the volumetric object. The smaller the cell size, the finer the resolution. Just as a bitmap image can reveal more detail when zoomed in if it contains a lot of pixels. The cell size parameter is necessary in order to keep the RAM usage under control. So the final RAM consumption is not influenced by the number of particles in your simulation, but instead on the number of cells which are created at render time which define the resolution of the volumetric object.