Convertibility:  Scalextric and Carrera use the same track system for both conventional and digital racing, so you can readily convert your layout from one kind of operation to the other by removing all the special track sections and other components related to digital operation and replacing them with those needed for conventional racing, or vice-versa.  The digital cars will run on a conventional track, though they may not have dynamic braking.  With Scalextric, especially, cars are easy to convert from conventional to digital by installing the necessary digital chip. In some cases this is an entirely plug-and-play operation. This allows you to start with a simpler, lower-cost conventional system and transition at relatively moderate cost to digital later on.  You can also convert a digital track to conventional if you find that digital racing is unsuitable for any reason.  SCX, however, uses two entirely different track systems.  Its digital track system has many good features, but converting from SCX conventional to digital or vice-versa means starting over from scratch. 

Interoperability:  One major drawback to digital racing, as it presently exists, is that none of the available digital systems are compatible with each other.  You can’t run one manufacturer’s digital car on another’s digital track without converting it to the other manufacturer’s digital system by swapping the chip modules.  This will require electrical soldering and often requires modifications to the car’s chassis, also.  If you want to own and race a large number of cars from a wide range of manufacturers on a digital track you will be faced with the need to install the appropriate digital chip in each car at about $20 per installation.  By contrast, any 1:32 scale RTR car will run on any manufacturer’s conventional track and power system with, at most, some minor trimming of the guide flag to adapt to a shallower slot.  Cars may not always achieve optimum performance with another manufacturer’s power supply and controllers but they will run reasonably well.  And, of course, cars from the many manufacturers who don’t make sets and track will run on any of the conventional track systems.