shell removes spaces, tabs, and newlines (that is, whitespace characters) from the command line and then cuts it up into arguments
$ echo one           two      three   four #one two three four

#!/usr/bin/env sh

v=$(seq 1 3)	#perfectly ok
v= $(seq 1 3)	#assign v with space, then 1 2 3 since 1 is NOT a command, it will return 1 not found
v =$(seq 1 3)	#v is a command and =$(seq 1 3 ) are 4 postional parameters

foo(){
echo $1
echo $2
echo $3
}

foo =z + 2	#=z + 2