Because they only had a small number of seats, they were never able to significantly influence politics. They may have had some influence within their faction, especially in clarifying certain issues and thus moving the faction in a certain direction.
I think the impact was still quite significant, especially in the beginning. If you are the first to worry about something, you can force the rest to respond in one way or another. Look at the Party for the Animals in the Netherlands. Since this party came into being, all the other parties have included something about animal suffering in their programmes.
A small party cannot decide policy, but it can put topics on the meeting agenda, which means that other parties have to say something about the topic. This forces them to think about the topic so they can take a stand. Even if they think it’s all nonsense, they should still care about it, but most will try to present themselves as best as they can on every topic.
I think the Pirate Party’s influence on European politics is clearly visible. The GDPR/AVG is heavily influenced by the Pirate Party, as are net neutrality, the end-to-end encryption debate, the right to repair, and the right to be forgotten. Now you can say that these topics were raised not only by the Pirate Party but by others as well, and this is exactly my point, the Pirate Party put topics on the agenda and found political supporters.
But I think we have seen enough time in recent years that we as residents can put pressure on our EU politicians. In Brussels, it is not only big corporations that exercise power, citizens are also listened to.
I don’t know if I would call this an example of what I just described, but it’s funny that this is the Pirate Party’s position. The party says modern technology makes a more direct form of democracy possible and has also experimented with this.