The more pure your sample is, the easier it is to interpret the results, as contaminating proteins may contribute to your overall signal in bulk measurements.
Differential Scanning Fluorimetry (DLS), Circular Dichroism (CD) and Dynamic Light Scattering (DLS) signals are concentration dependent and additive. So generally, minor contaminants will be expected to contribute a low signal. However, there might be specific cases where the contaminate contributes more than you might otherwise expect to the overall signal, due to protein structure or mass. When comparing samples, similar purity and concentration between the samples will help mitigate potential artifacts.