Let me paint a picture for you.
You're on the last mission of the game. You're taking your sweet time, carefully jumping over the platforms and obstacles in your way. With your palms sweating and eyes focused, you slowly move the control stick towards the goal. You come across the last obstacle. Your body tenses up. Your breathing grows heavy. In a moment that could make even the most hardiest of cardiovascular surgeons sweat, you manage... to slip and die.
You're a little less tense this time around. You jump over the platforms and obstacles with ease. Once again, you're face to face with the last obstacle. Your palms are more relaxed but your eyes are still focused. You carefully move the control stick to complete the last maneuver. You die.
You take a short breather and gather your bearings. You begin. You breeze through the obstacles — you're a professional at this point. You stand once more in front of the last obstacle. Angrily, you slam the control stick in the intended direction. You die.
You don't reload.
You turn off the game, not wanting to go through the obstacle course again.
No matter how easy a part of the game might be, poorly placed checkpoints can ruin the player's entire experience.
If I have to follow the car for five minutes one more time...
The most annoying games are the ones that make you go through an extremely long and enduring sequence, only to have you repeat it if you die. It's disgusting.
GTA IV and San Andreas are two titles that instantly come to mind.
Poorly placed checkpoints show poor design and planning from the developer.
During car chases, taking a wrong turn or missing an exit meant I would have to restart the entire mission, regardless of how close I was to finishing it. Dying would set you back so far, and it marks the moment easy and "fun" sequences start to become boring and repetitive.
Unfortunately, this problem isn't only prevalent in the GTA series. Poorly placed checkpoints are practically everywhere.
In COD, dying meant you had to repeat a sequence over and over.
In order to fix this, developers should include different checkpoints throughout missions. GTA V did this perfectly. If you were unlucky enough to die during a mission, GTA V gave you the opportunity to directly spawn at a previous part of the mission, not the very beginning.
Making different checkpoints throughout the mission should be something all games do. Those fun, and easy parts soon become tedious if a player constantly fails to succeed.