I was looking at the card sensor team, (spend a die to change a die to accuracy) and was wondering when do you use a card like this? Do you use it before you roll, and roll one less dice, or do you use it after a roll and change, lets say a blank side to an accuarcy side?

Its after, just like in the fleet building preview, how they used screed.

EDIT: And what your doing is removing a die of your choice you rolled, and changing another to an accuracy. Its a bit situational, but for the victory class, can be effective, because of its 6 die attacks.

The sensor team is really about insuring that a good attack roll doesn't get mitigated by the half-damage token (Brace?).

Say you have a VSD-I that will do a ton of damage when it can roll its black dice, but will not generate accuracy results regularly. If you get a good roll when using concentrate fire, you could very well be getting 8+ damage (14 is the technical maximum, and ludicrously unlikely) so a brace token will be mitigating 4 or more damage. Being able to add an accuracy to such a roll, even if you are sacrificing a hit rather than a blank, would be superior to adding more damage in most cases.

Most upgrades in Armada seem to be about increasing the lower bound of damage a ship will do, or making it more likely that a big hit gets through, as opposed to being a straight damage buff in all circumstances. Only things like Dominator and Extended Magazines are real straight damage buffs, and they are very expensive, and have major drawbacks and limitations.