Before it
8-bit quantization worked; 4-bit lost too much accuracy to be usable.
The problem
Even 8-bit weights leave the largest models out of reach of a single GPU.
What it introduced
One-shot second-order weight rounding that holds accuracy at 3 to 4 bits, in a few GPU hours.
Why it matters
4-bit is what makes a 70B model fit on consumer hardware. This is why local inference is possible at all.
What modern models inherit
The 4-bit quantized checkpoint as the standard local format.
What came next
AWQ traded a different accuracy-speed point; GGUF packaged quantized weights for llama.cpp.