Nanolasers and nanoLEDs are seen as potential sources for low-power optical interconnects. The enhancement of the spontanous emission rate (Purcell effect) related to the small volume has been perceived as a key aspect in the operation of these devices. The fundamental aspects of size scaling in practical nanolasers and nanoLEDs will be discussed in this talk. Firstly, experimental results on nanoLEDs coupled to waveguides on Si will be presented. The effect of surface recombination will be discussed, together with promising passivation methods. In the second part of the talk, a simple theoretical model based on rate equations will be used to investigate the ultimate limits to scaling. In this model, spontaneous and stimulated emission are treated on the same footing, leading to a consistent treatment of the rate enhancement due to the decreasing volume. The analysis shows that Purcell enhancement of spontaneous emission plays a limited role in practical structures, due to the unavoidable linewidth broadening, while the related volume dependence of the stimulated emission rate has a key impact on nanolaser dynamics.