The truth is one interest leads to another and so on. Every thing learned in one medium can help compliment another. For example: proficiency in drawing and then learning the properties of cutting glass can lead to being able to create your own stained glass patterns. For me those lead to mosaics so I could do something with my scrap glass.
Original mosaic design by ColtPixy 2006
I like learning new things. Just doing the same thing all the time would not only be boring for me but it would also limit my abilities in my chosen medium.