The "marks to hit for straightaways or (...)" are visual indicators on the sides of the track, showing the distance to the corner. Part of what makes these drivers the best in the world are that they're able to hit -- mostly -- the exact same braking spot coming from 300kph down to 60kph lap after lap after lap, without a computer telling them when to brake.
Coincidentally, that row of LEDs on the top of the wheel is supposed to tell drivers when to shift, but teams found out a long time ago that the visual indicator wasn't being processed fast enough by the drivers' brains, so now drivers get a little beep in their ear when they're supposed to up/downshift.
I'd wondered where those went, it's amazing what they optimize to buy milliseconds per lap.
Not to mention that the precise limits of what speed can be achieved where will change as track temperature and conditions change. By giving that to the driver, they can use their intuition to tune their optimal lap performance.
It's easier to memorize every cornering speed for every corner in the circuit than trying to 'feel' it every time.
It's quite interesting to watch cockpit cams and see the effect any little mistake or different line has on the lap time. You can also often see differences in brake balances between drivers and more on them during the race, can be really interesting if you pay attention to that.
There is even a type of penalty, the "drive-through" consisting on driving the whole pit lane without exceeding the speed limit.