Can you provide examples? Ideally of both positive and negative outcomes.
Otoh lots more information available to the public often also makes it easier to detect lying and corruption.
It concerns me more that "politician" is a very ambiguous word. Basically everybody active enough is a politician, even though he may or may not be in senate, belong to some party and such. And an open dataset on "pretty much everybody" seems a bit more questionable than on those we consider "being in charge".
In practice, aggregation services like this tend to have more benign results like enabling the bulk emailing of politicians. Others include the suspicion that the popularity of Theyworkforyou, a UK site run by the same people which parses open data on parliamentary speeches and votes, might have had the effect of encouraging MPs to make brief, inconsequential speeches in order to boost statistics on their relative activity in Parliament. Another area in which the effect of their data aggregation might be considered questionable is where it's used as an authoritative source that a particular MP is "strongly against" a particular "cause", when in actual fact they may simply have voted with the party line against a particular bill related to that cause purely due to concerns about one specific aspect of that bill.