Playing the first at the Stadium is great for us. I haven't been following too closely this season, but as far as I know our performance improves a lot at home. We have been disappointing away.
In tournaments, playing the 2nd match at home isn't necessarily an advantage per se.
The general rule is that when a team gets a favourable result in the first match, this team goes to advance the vast majority of times. Reversing a negative result at the first match, either at home or away, is always the exception.
In our case, if the first game were away, given our poor perfomances when out, chances would be Barcelona would build a good or very good result, practically sealing their qualifying to the semis.
On the other hand, at home Juve has a decent shot at having a first good result, or at least decent, and go to Camp Nou with chances. That's what we want.