Flight search platforms are useful, but how could they, alone, truly quantify the impact of local events on your trip? They are excellent for finding the lowest prices for a flight to Porto, but will never tell you if the São João festival will make the streets impassable or cause hotel prices to spike.
We're talking about an information asymmetry: the website sees seats, not the crowd. For maximal optimization, you need to seek local information well beyond, such as checking the municipal festival calendar or football match schedules for a full expression of your stay's potential. Relying solely on these tools for on-the-ground details leaves a huge margin for the unexpected.