If the total bid is high (12 or 13), Spades players usually try to set their opponents. Sometimes, though, players will duck tricks to avoid taking bags.
No matter what the total bid is, you should be attentive to satisfying your team's bid. It's not so serious to get set if each partner has bid 1. You will only lose 20 points. As your team's bid increases, getting set has more serious consequences for your team's score.
Here is a video clip that shows a player refusing several opportunities to take an extra trick in clubs, even when there's a signal that their partner might not make their bid. The total bid is 12, so there will be 1 bag, and both sides should be looking for opportunities to set the opponent.
This is a replay of that hand, where you can see that West (Johnny) repeatedly ducks clubs tricks. Instead, West should have been looking to take extra tricks because East's King of Hearts was taken early in the hand. This was a trick that East was probably counting on taking because
Note that the opponents, North and South, collected 2 extra bags. This may eventually be harmful to their score, but the game may finish before it can hurt them. This shows how getting set has an immediate, detrimental effect on your team's score, as opposed to collecting bags, which is only harmful in the long run.