You've just bought the latest title but your PC's a bit long in the tooth. Say you bought the machine two years ago with a reasonable graphics card included.
You start the game and marvel at the graphics but before long, a feeling of 'incompleteness' washes over you. Maybe it's the framerate, maybe it's the shadow quality - you know what you have to do, you enter the graphics setup screen.
Your worst fears are realized - your PC is apparently borderline obsolete. You persevere. You spend time comparing various settings. Reduce the shadow quality, reluctantly reduce the draw distance, turn down texture quality, increase texture filtering. You Google for tweaks and apply them. Seems lots of people are complaining about performance. Someone has a tweak but it turns out to be bullshit. At least for your config. One or two tweaks have some effect but you have to spend time getting them just-so. Meanwhile the graphical heights you know the game's capable of remain unrealised. It becomes an obsession. Short of spending the money to upgrade, you play through the game but it's not a 100% experience and it eats at you.
Afterwards you load up a good old game from a few years ago. Everything's maxed. Sure, the graphics aren't a patch on the latest DX masterpiece, but it doesn't matter - you know you're getting the best from the game and you enjoy it for what it is. What are ya gonna do?