This is completely dependent on context. For example, in business writing the goal is to use language that is clear, concise, and able to be interpreted as quickly as possible. In the workplace it is of the utmost importance to avoid miscommunications. Time is money after all.
On a similar note, in academic writing (such as research papers) it is important to adopt a formal tone while continuing to be as succinct as possible. The goal is to be as professional as possible while presenting as little fluff into your work as possible. Instead of saying "The problems that came up during our research were clearly caused by things we did not think about.", you might say something like " Issues faced during the research were caused by external factors unaccounted for."
There are plenty of other examples in writing, but the most important thing to account for is your audience. If you are writing a children's book, a letter to your uncle, or a book on nuclear fission for professionals you will know how to properly adjust your vocabulary. The same idea applies to speech; however, if you enjoy using an expanded and elevated vocabulary do not let anyone else dictate how you speak in your day to day life. If you are interested in this topic I recommend researching code-switching!