XSL recursive call - xsl:functions vs xsl:template with call template

I have basic query. I have been using xsl:template and use call tempate to make recursive calls to the template. I see xsl:function which also has feasibility to make recursive function calls like recursive template calls and achieve the same. When should xsl:function be used and when should xsl:template be used. I am not sure what is the diffence between the two and when should they be used. What are their special features of each of them. Can someone please help me understand this better.