It is always better to use simple language when writing, but it also depends on what is writing. Imagery is important to storytelling, for example, but if one is just sharing information it is best to just stick to the facts with as much clarity as possible. Native English speakers in America have a lot of problem with writing though, so someone who is learning shouldn't feel too bad if told their writing is a little wordy or too full of modifiers. A lot of people write the way they speak, and I am sure that is the case in any language.