You write information messages to the console that cannot be easily suppressed.

[Moran79]

You write information messages to the console that cannot be easily
suppressed.
It is more R like to generate objects that can be used to extract the
information a user is interested in, and then print() that object.
Instead of print()/cat() rather use message()/warning() or
if(verbose)cat(..) (or maybe stop()) if you really have to write text to
the console. (except for print, summary, interactive functions)

I got the email above from Ben. I used cat a lot in my package, and I finally decide to follow the verbose type.