Conversion to tB transforms data into the log scale. It is not mandatory, but helps visual interpretation and also statistical evaluation, because the histogram gets a Gaussian distribution.
An example is given here: Classification Sentinel-1 problems with MaxVer
More information here: https://publikationen.uni-tuebingen.de/xmlui/handle/10900/91317?locale-attribute=en (page 35)
So it depends on your application if it makes sense to convert to dB or not.
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