para vs. a

Is there any difference in meaning between using "para" or "a" in a sentence like the following: Siéntese __para tomar__ un cafe Siéntese __a tomar__ un cafe I had learned the to use "a" in another course, but in your course you say to use "para". Is the difference simply stylistic? Is it a regional difference? Is one is more formal or more polite? Thanks.

I'm not really sure, but I think that you would use "para" to say "in order to"; to emphasize the purpose, the goal of the action, to say why he should sit down, what for. While "a" is just to say: Sit down to have a coffee. without emphasizing anything. Es solo mi opinion, no estoy seguro.