Do u think google calendar useful and convenience?

my cell has a program having the similar function with google calendar(and i think most of cells have that type of program),I use it most time but not google calendar, cause I take cell with me every minites,so when its necessary then i can update my plan at anywhere anytime,in contrast,google calendar is not that convenience,
and now google calendar send me a text everyday and its free but looks like it also cant make my life a little more convenience,someone said google calendar have a huge future,maybe i just mistake something,how do u use google calendar?