The purpose of the article is to analyze the feasibility and capabilities of the Industrial Internet of Things (IIoT) sensors in IoT-based control loops; the focus is on the latencies of these systems, as related with the maximal sampling frequency in the loop. We discuss, under simplifying assumptions, with examples, several issues related to the latency of the IIoT control systems, especially those supposed to operate over large distances and in real time, and we show that fast and constant sampling rates allowing fast control are not possible.