Fair question -- convenience, mostly. it's a combination of things.
Primarily the display -- the radar and satellite pictures are
full-screen and animated. Another factor is convenience -- it's all in
one place, and you can, for instance, easily page through wind,
conditions, temperature/dewpoint maps, etc. Also, you can specify a
route and it will give you maps, radar, lightning, METAR/TAF data, etc.
along the route.

Wiz