Thermal analysis techniques are routinely applied to characterize the thermal behavior of metal organic precursors used for oxide film preparation. Since the mass of films is very low, researchers do their thermal analyses on powders and consider that the results are representative of films. We will show here that, in general, this assumption is not true. Several examples involving precursors of YBa2Cu3O7-x (Ba and Y trifluoroacetates and Ba propionate) will serve to appreciate that films can behave very differently than powders due to their enhanced heat and mass transport paths. Ultimately, we will demonstrate that, in some cases, relying on powders thermal analysis may lead to erroneous conclusions.