Have you seen this happen in an automotive application or is that comment based on general principles of vapor compression refrigeration?
In our applications, the lower limit on high side pressure is the fact that a lot of HVAC-R compressors use the differential pressure instead of an oil pump as the motive force for internal lubrication. In our most energy-conscious applications, we have used a setup that actually turns the compressors off and uses a pump to circulate refrigerant at just enough pressure to feed through the expansion device. With the design practice used in the refrigeration industry that corresponds to about a 50°F saturated condensing temperature.
Never seen it happen, no. But it is one of the driving reasons as to why larger systems, like whole house A/C units (especially ones that double as heat pumps) often use an expansion valve versus an orifice tube like an automotive A/C.
With an orifice tube, the flow rate through the tube is limited by the viscosity of the fluid, the current low/high side pressures (which depend on a number of factors), and the size of the orifice.
However, an expansion valve, especially ones with external control, can usually more effectively meter out the refrigerant to optimize COP, output, and energy consumption.
An automotive A/C isn't generally designed with high efficiency in mind. Compared to a building A/C, it really only spends a small time of it's existence actually running. Over the lifetime of a 150,000 mile car, it may only run 2,000 hours before being scrapped. A building A/C might see more like 30,000 hours of operation over a 15 year service life, so efficiency is far more important.
In other cases, especially with small appliances like refrigerators and dehumidifiers, the high side and low side temperatures are usually quite predictable within a small range, and the compressor runs at one speed. In these cases, the ideal throttling can be calculated within a small band, and a properly sized orifice throttle can be used with very little loss in efficiency.
If I recall correctly, I think there are a few cars that actually do use expansion valves instead of orifice tubes. There probably would be a noticeable gain in efficiency if a proper control scheme could be drawn up. But in most cases, the engineering time and parts cost of such an improvement is going to eclipse the fuel savings (or profits, if you are an OEM).
I think the future trend will be more towards electric A/C compressors in automobiles. They can be very easily controlled, are not subject to variations in engine RPM, and will be more attractive to buyers looking at HEVs, PHEVs, and vehicles with auto stop-start. (Plus the obvious EV and EREV applications.) Even though there is a significant amount of energy lost in the conversion from mechanical to electrical back to mechanical energy, the vast improvement in the capability to control its function allows for far greater efficiency gains than simply modifying the fully mechanical system alone. This is also why OEMs are increasingly using electric power steering (or sometimes EHPS), electric fans, and even electric water and oil pumps.
