Heat transfer fluids (HTFs) are critical in numerous industrial processes, enabling efficient heat exchange and precise temperature control. HTF degradation, primarily from thermal cracking and oxidation, negatively impacts system performance, reducing fluid lifespan and increasing operational costs, thus necessitating regular monitoring and proactive management. This review assesses optimal sampling frequencies for organic and synthetic HTFs, considering degradation mechanisms, relevant analytical parameters, and the economic advantages of proactive monitoring. The objective of this review is to examine HTF degradation mechanisms, compare organic and synthetic fluid properties and their impact on sampling frequency, and discuss strategies for optimising system performance and extending fluid life through effective HTF condition management. The article highlights the importance of fluid management, including appropriate fluid selection, to optimise system and fluid health, which is crucial for maximising their lifespans, ensuring safe operation, and minimising costs.