Error with Adobe Illustrator when using Bristle Brush paths and transparency

Hello Experts,
I was using Adobe Illustrator to do artwork when I was saving my file, I got this error message. I did use a lot Bristle Brush paths and transparency. I just pressed the button OK, and it seemed to work fine. Did I do something wrong?
I hope someone from this forum would clarify the message.
Thanks.

Adobe Illustrator
The document you are currently printing contains multiple Bristle Brush Path with transparency.
A large number of such objects can make the document too complex to print. You can reduce complexity and retain appearance by selecting Bristle Brush paths and rasterizing.
