3D printing and internal geometry/intercepting faces?

So I have been modeling the Blender for a few months now, and want to start learning how to print what I model on my printer. I been getting mixed answers about this so I hope to get a final answer.
I was wondering if its bad to have internal geometry and/or intercepting faces for 3D printing it?
I was told that as long as there’s no holes or weak/thin parts, its fine for printing. Since whatever you see rendered, is ok to print. Is that true?

Hi, It has been a while since you posted, but since no-one has answered yet, I’ll jump in.

Depending on the slicing software you are using, you can often get away with some intersecting faces and internal geometry might create a void inside your model. Check the result in your slicing software before committing a time-consuming job on your printer.

I have found that intersecting faces sometimes confuses the software if you are uploading your model to one of the on-line print services. If you find that the on-line tools are reporting thin walls or other issues and you can’t see why, intersecting faces is often the cause.