all_coeffs() can be sometime better than using coeffs() for a Poly.
The difference lies in output of these both. coeffs() returns a list containing all coefficients which has a value and ignores those whose coefficient is 0 whereas all_coeffs() returns all coefficients including those whose coefficient is zero.
>>> a = Poly(x**3 + a*x**2 - b, x)
>>> a.coeffs()
[1, a, -b]
>>> a.all_coeffs()
[1, a, 0, -b]