Cheap TVs are edge lit. Usually at the bottom edge only but sometimes top edge too.
So let's say there is a scene with bright light at the top right but rest of scene is dark. In order to light that part up the leds at the bottom right need to be turned up a notch which bleeds across the whole screen.
With FALD you have the whole screen split into zones. So only the zones which need bright light or colours get turned up. This means black bars and dark parts stay dark and only the bit which needs the brightness gets turned up.
However in scenes like Gravity where it is mainly dark and stars which need lit up even a FALD TV can have noticeable bleeding if it doesn't have enough zones.
The FALD TV I have has around 50 zones and its regarded as one of the top 3 TVs to buy in 2018 in terms of value for money. The other 2 being an LG oled and a edge lit TV NU8000.
However my mate at work has a FALD with over 1500 zones from the same company (Sony) and it is 75" he bought it when it was reduced from £3500 to £1900 when it went EOL.
I've seen his in action and before I saw it before my eyes I didn't believe LCD could compete with an OLED. The oled is still better overall but the gap isn't as big as people make it out to be.
If you dont game much or at all and are looking for a 55 or 65 inch screen get an oled. However if you want to spend less or want a bigger screen then FALD will be the one to go for.
I got mine in a sale 55" for £999 the 65" is now £1299 I wish I had waited another 4 months and gotten that but it's for the games room so no big deal as a 65" would dominate the room especially as I only sit a metre or so away.
OLED also has drawbacks when it comes to screen size. As in if you want a 43" TV you cannot buy an oled. They are only made by 1 manufacturer LG who sell panels to others who make their own electronics for them. Same as cars like the new Mercedes has a Peugeot engine in it. So Sony, Panasonic, Phillip's etc oleds are all LG panels. That is why they are so expensive 1 manufacturer.
I'm waiting for a 55" 4k hdr oled available for around £1k next year around January before I buy an oled for the bedroom.