Hiya!
I'm a DM, I enforce them...in 1e/2e/HM. In 5e I "encourage" them. In my 5e game, if it has a specific gp value, you must have it; it is also consumed/used in the casting. For other components, your generic focus/component bag will get you through. HOWEVER...if you actually *have* the specified component(s), you can use those and they get used up, but that spell will have at least average effect, or double range, or increased duration, or wider area of effect, or you can manipulate some aspect of it. For example, a fireball spell with actual components on-hand will do at least 4 points per die of damage (if you roll 1-3, it counts as 4).
This encourages the caster to actually seek out components and all that other cool magical stuff, but doesn't penalize those who don't care or who have characters with 'supplemental' casting (like a Paladin, for example).
But in my 1e/2e/HM games? Hell yeah! You don't have the component...you can't cast the spell. Feel free to supplement seagull poop for bat guano, however, I love a good random roll on the Miscast table.
^_^
Paul L. Ming