Carbon-reinforced soles combine a nylon base with a carbon fiber plate or inserts in key areas, giving you most of the stiffness benefits of full carbon at a lower price point. For the vast majority of racers and performance riders, this is plenty stiff — you'll get solid power transfer without the harsh, unforgiving feel that full carbon can have on long rides.
The real advantage here is the slight compliance that nylon adds. Full carbon soles can feel brutally stiff, especially over hours in the saddle or if you have sensitive feet. Carbon-reinforced gives you a touch of flex that can actually improve comfort without noticeably sacrificing efficiency.
Go with carbon-reinforced if you're racing or training seriously but don't want to spend top dollar, or if you've found full carbon shoes too harsh on longer efforts. Full carbon is really only worth it for elite racers chasing every last watt.