Suggested

Back markers

They do, depending on their pace, the slower they are the less time you loose. You first loose a bit of time due to dirty air and finally overtaking, given their pace is at that moment not too far off then half a second is quickly lost there. If they are pretty close, as within a couple of seconds behind in lap time, or it's a track with particularly bad dirty air, they can be even nearly impossible to overtake without using Boost/DRS, hence the occasional request/suggestion for blue flags. Though with groups or quite a lot of cars spread around the track it's less noticeable as everyone is fighting through those areas of dirty air and thus struggles equally.