Can I not rely on append only allocating when the values to append won't fit in the remaining capacity of the underlying array starting from the end of the slic

Can I not rely on append only allocating when the values to append won't fit in the remaining capacity of the underlying array starting from the end of the slice? Some articles indicate this and definitely don't seem surprising [0]. Granted I don't know the implementation details, but how do copies of the array or numbers of slices of the array affect that? Regardless, with Go as opposed to lower level languages, building reliance on whether functions do memory allocation (even built in ones) is folly. 0 - https://blog.golang.org/go-slices-usage-and-internals https://blog.golang.org/go-slices-usage-and-internals