Function: Inflectional affixes primarily serve grammatical functions, expressing grammatical relationships or indicating aspects such as tense, number, case, or comparison.
But sometimes, categorisation can take place without affixation, and when this happens, we call this type of categorisation zero-derivation, or conversion.
Productivity: Derivational affixes may have more limited productivity compared to inflectional affixes, and their application can vary across different words and contexts.