A Simple Limit
A common request from clients is that they want the product to look clean and simple. That's also my goal. I love symmetric, sharp, and neat interfaces. However, how does it translate to users?
Clean and simple is irrelevant if it stands in the way of them achieving their goals. People will have a pain point that they want to solve with your product. So, you show them that you're the one that solves that problem. And then you worry about looking clean and simple.
The way something looks is a decisive competitive advantage. It makes people choose your product. On the other hand, how something effectively solves people's problems makes them become users.
Make sure you understand what they came to solve with your product. Make your product communicate it (tutorials are not part of the deal).
Once that's in place, go on and make it pretty until your start hurting that conversation. Stop right there. That's the simple you should aim for.