The Philosophy Toolkit

One of the things that really interested me in this toolkit was section "Types of Definition", under "Logical Terms". Until last year I believed there was only one type of definition, but the toolkit mentions four types: lexical, stipulative, theoretical, and persuasive. Lexical definitions are used to clarify something, and are the types of definitions typically found in dictionaries. Stipulative definitions change the meanings for already existing terms. Theoretical definitions try to further the meaning of a term by proposing different hypotheses. Persuasive definitions try to "fix" the meaning of a word rhetorically. Personally, I don't understand the need for all of these definitions. I have always gone by purely "lexical" definitions, and that has always worked well for me. When working in Philosophy, one of the most important things is for everyone to understand the meaning of the terms being used. Wouldn't it make more sense, then, to work with the same lexical definitions instead of constantly having to change them, or make up new ones? Stipulative definitions don't seem to make any sense at all; how can one simply up and change the meaning of firmly established terms? That just doesn't seem right. And although I think it's great to try and elaborate further a definition, I don't think the elaboration should count as a new definition itself. And, quite frankly, I haven't the slightest idea of what purpose a "persuasive" definition has. What is the real purpose of any of these definitions? Are they truly essential to understanding a term, or is it time to let them go? I stand by the idea that a firm lexical definition is all we really need.