Understanding Distillation is still important for Chemical Process Development and Organic Synthesis At Scale.

One of the non-obvious outcomes of structural identification using spectroscopy (particularly NMR and MS) is reduced experience with distillation among organic synthetic chemists. This is because even an inexperienced student researcher can now routinely identify a substance using milligrams of a pure compound; first using flash chromatography. Then high-performance preparative liquid chromatography or preparative gas chromatography can replace old-fashioned distillation for making samples big enough for identification of the products from most steps in laboratory synthesis. 

Corroborating this trend is the virtual disappearance of boiling points as part of physical characterizations in the chemical literature.

Finally, as the catalogs of suppliers of chemical intermediates become thicker, more of the products of early steps in syntheses can simply be purchased. It is these lower molecular weight entities that formerly were prepared and distilled in the lab.

Standard distillation has an inherent problem that became a further reason for the substantial abandonment of distillation from the laboratory. Unless a small-scale distillation column receives an input of heat supplied by vigorously boiling the liquid mixture in the still pot, it cannot achieve liquid-vapor equilibrium. Thus, on the lab scale, there is a hold-up of distillate that is inevitably lost and this can be up to 30%. Compounding this inherent difficulty is the annoyance that all glass laboratory distillation equipment is expensive and does not easily accommodate the particular amount of crude that you may have. That is, the amount of crude distillate must be selected to fit the size of the physical assembly that you have and not the other way around. Fractional distillation assemblies are not available in your lab drawer in 100 ml, 200 ml, 500 ml, 1L, 5L, and 15L sizes like round bottom flasks are!

The days when distillation units were patched together with hardened cork or rubber stoppers between pieces of blown glass are long past. Now all glass assemblies are a single piece or pieces joined with ground glass joints.  

Because of this, now more than ever, distillation assemblies for vacuum distillation often use the same equipment as for simple distillation and lab workers don’t appreciate the special requirements imposed by the low-pressure condition. The boiling point of the fluid mixture in the still pot of a distilling assembly depends upon the pressure at the surface of the liquid, not the pressure recorded on a pressure gauge, which may be, and usually is, closer to the vacuum pump. For pressures from 760 mm down to 15 mm of mercury, a regular distillation flask is satisfactory. For pressures below this level, and particularly pressures 2 mm or less, the diameter and location of the vapor port linking the distillation portion of the apparatus to the condensing portion become very important. This is not usually understood.
The increment in vapor pressure at the surface of the boiling liquid, over and above the vacuum pressure reading taken at the receiver is proportional to the length and inversely proportional to the fourth power of the diameter in centimeters of that sidearm plus any other narrow portion of the path between still pot and condenser.