Brace expansion using {...} can reduce having to re-type similar text and automate combinations of items.
This is helpful in examples like:
mv foo.{txt,pdf} some-dir - moves both files
cp somefile{,.bak} - expands to cp somefile somefile.bak
mkdir -p test-{a,b,c}/subtest-{1,2,3} - expands all possible combinations and creates a directory tree
echo {0..50} - echos all numbers from 0 to 50
echo {a..c}{1..3} - echos all combinations (a1, a2, a3, b1, b2, b3, c1, c2, c3)
Brace expansion is performed before any other expansion.