There are pro's and con's to BOTH.
Grand Piano Cons: Space, requires maintenance and some of which that costs such as tuning. If you move, it costs even more. Due to noise/loudness it can cause issues if you live in an apartment. Extreme cost disparity - $1800 digital piano compared to an $18,000 grand piano... And not everyone does, but you SHOULD care about acoustically treating the room. More $$$.
Digital Piano Cons: Drastically inferior sound, inferior action, and it doesn't make a room as beautiful like a gorgeous, shimmering black grand can. Although this isn't as long as the aforementioned list of cons, sound and action are thee most important factors of a piano. Period.
Nothing can beat the real thing, however, in a world where things must be practical, and you're not rich - a digital piano can't be beat either.
Shyyyrrryyuuuken!

Ashton