It does indeed produce much smaller binaries, including for macOS.

  yuriy@MacBookAir ~/t/tinygo> time tinygo build -o test-tiny main.go
  
  ________________________________________________________
  Executed in    1.06 secs    fish           external
     usr time    1.18 secs    0.31 millis    1.18 secs
     sys time    0.18 secs    1.50 millis    0.18 secs
  
  yuriy@MacBookAir ~/t/tinygo> time go build -o test-normal main.go
  
  ________________________________________________________
  Executed in   75.79 millis    fish           external
     usr time   64.06 millis    0.41 millis   63.64 millis
     sys time   96.76 millis    1.75 millis   95.01 millis
  
  yuriy@MacBookAir ~/t/tinygo> ll
  total 5096
  -rw-r--r--@ 1 yuriy  staff    74B  3 Apr 19:17 main.go
  -rwxr-xr-x@ 1 yuriy  staff   2.3M  3 Apr 19:18 test-normal*
  -rwxr-xr-x@ 1 yuriy  staff   192K  3 Apr 19:18 test-tiny*
  yuriy@MacBookAir ~/t/tinygo> cat main.go
  package main
  
  import "fmt"
  
  func main() {
          fmt.Printf("Hello world!\n")
  }