You mean the meanings of words?
The ability to use another somewhat similar, if less common word, for variety or accuracy, or to convey a slightly different shade of meaning, texture, or emotive reaction, when you want to, rather than be limited/constrained to just a few scant, limited words that you already know?
.
Important for what?
Depends on your purpose, I guess, speculate, summise, ponder.
:)