You most certainly know the seat maps that allow you to choose your seat during check-in. Some airlines provide very detailed seat maps, some don’t and you are left to randomly chose one. seatguru solves this. Select the airline you’re flying and the aircraft type and you get a detailed overview which seats are ‘good seats’ and ‘bad seats’.
With a little luck you get a seat with plenty of legroom instead of a seat in the vicinity of the restroom…
Quick note: I am not affiliated with seatguru, nor got paid for this article. I just like service.