Usually, the second index is optional. If you remove it, you might improve code readability.

Example:

var a []int
a = a[0:len(a)] // `a[0:len(a)]` is the same as `a[0:]`

You can apply the Remove redundant index quick-fix to such cases. After the quick-fix is applied, this code looks as follows:

var a []int
a = a[0:]