Hi,
One other difference between the 99 cent light and the 100 dollar job?
Once you've had your first 100 dollar light, you'll not only want more(!), but you'll never be caught dead with one of the plastic 99 centers ever again.
I bought a NightOps Falcata about 2 or 3 years ago, then I found a Gladius (also NightOps), and a Wolf Eyes M90 and I currently have a pending order for:
6MAX HO Cree Explorer
D2A Defender Tactical
EagleTac P10C2 LED
Fenix TK10 Q5 Cree LED
Wolf Eyes 9TX Raider
all from PTS.
The thing is really, that yes, a 99 cent keychain light might help you find your door lock at midnight and it might locate your keys for the lock - but a good solid light is so much more reliable and versatile.
Some lights are very effective self defense tools, others put out way more light and for much longer than any other, making roadside repairs easier and safer.
Some people, like myeslef work in fields that require us to enter dark places at weird hours in all sorts of conditions and there are many companies that offer specialty lights for that purpose.
I warn you though - the bug is easy to catch! That list I mentioned above pales in comparison to most of the lists other members could post of what they already own. If you have even the slightest hint of an addictive personality in you, I suspect you may end with a pack full of lights before the year is out!
Good luck - and welcome to the forum!