If you're writing for someone else, it's important that you write in their "voice" and capture their brand. Anything less, and you might confuse the readers, and compromise what you are trying to communicate on their behalf.
But, if you are doing your own writing, you must communicate like YOU, or once again, the reader will be confused.
Capturing someone else's voice can be difficult, but sounding like yourself, well, that should be relatively simple.
But, the sad truth is that many people write content that doesn't sound in the least bit like they sound. The words and tone they use make the content unbelievable and difficult to relate to, and that's pretty much exactly what you DON'T want to do.
When people read your content, you want them to say "that's sounds exactly like you" or "I could hear your saying those words."
When you sound like someone else, the reader doesn't know what to believe, and their skepticism is just about the last thing you want to generate with your writing.
My tip is to take a step back and to write your content just as if you were speaking. Don't worry about grammar or sentence structure just yet; save that for when you edit. In fact, read it aloud after you're written it, and hear how it sounds.
Did you use words that you don't commonly use, is your tone contradictory to your personality, and are you coming across like someone else? If so, redo the content so that you don't sabotage the YOU that you want to present.
Be true to yourself, write in your voice, and enjoy the process.