I think that is awful advice.
Big words are great. They're linguistic accoutrements. They let you circumlocute in arguments without anyone noticing. Of course we should be parsimonious about it. Being overly ebullient will make for hard to read text, but that doesn't mean every word should be monosyllabic. As long as we excogitate before we stick something absurd it, it's all good.
"But they won't understand what it means!" I hear the literary editors cry.
Of course they won't - the first time. No-one is born with a superabundant vocabulary.
It's by reading new vocabulary that we learn - either by understanding it by context, or by looking it up or asking someone. When I first read big books with complex words, I had to ask my parents what they meant - which is a good thing. YA Lit especially can to evade the problem by being puerile and putting in language that frankly deserves to be kept to reality television involving people from Essex (Disclaimer, not all YA lit!).
The variety in our language(s) means that we can express ourselves in a multitude of ways. It makes life interesting. So don't stick to saying everything is 'nice'. Go gasconading about your phenomenal vocabulary, and take a trip down multi-syllabic lane.