Well, one thing is for certain: you can at any point decide to open and grade the cards, but you can’t do the reverse. So unless you want to grade them so you can sell them or put them in a set, just keep it sealed. It’s impossible to regret that, whereas you definitely could regret opening it.
Normally this is the case…but the 10th movie set is a little bit of an exception. The only seal is one of those sticky adhesive things, so you could take the cards out of the bag and the card file (inside they are in a sort of binder page, not sealed) and then reseal the entire thing. I’ve been burned on this in the past where supposed “sealed” card files actually had different cards than the original file or they were clearly in played condition.