Unless you KNOW that you can get away with it. Doing it vs D3 will get you grabbed EVERY time. Vs Snake will get you Utilted. Vs Ganon will get you murder choked -> tech chased.
Powershielding fireballs gives the opponent the advantage. The wind-down on it, especially grounded, is far too easy to punish. The best utilization for fireballs is to approach and space since you can follow right behind them at any given time. If they powershield it then, you still have a chance to get in your grab or spaced Fsmash before they put down their shield and have time to hit you.
Exhibit A: http://www.youtube.com/watch?v=OEfGB-VUzms&feature=player_profilepage
Fireballs' strength is that you force your opponent and react, and if you're right behind it, you can punish whatever action that is. It's like playing doubles with your partner in front of you and you're always in position to punish whatever the opponent does to him. They work for camping if your opponent doesn't powershield like he should, but I wouldn't do it...ever.
Powershielding fireballs gives the opponent the advantage. The wind-down on it, especially grounded, is far too easy to punish. The best utilization for fireballs is to approach and space since you can follow right behind them at any given time. If they powershield it then, you still have a chance to get in your grab or spaced Fsmash before they put down their shield and have time to hit you.
Exhibit A: http://www.youtube.com/watch?v=OEfGB-VUzms&feature=player_profilepage
Fireballs' strength is that you force your opponent and react, and if you're right behind it, you can punish whatever action that is. It's like playing doubles with your partner in front of you and you're always in position to punish whatever the opponent does to him. They work for camping if your opponent doesn't powershield like he should, but I wouldn't do it...ever.