  Exact RG equations are discussed with emphasis on the role of the anomalous
dimension $\eta$. For the Polchinski equation this may be introduced as a free
parameter reflecting the freedom of such equations up to contributions which
vanish in the functional integral. The exact value of $\eta$ is only determined
by the requirement that there should exist a well defined non trivial limit at
a IR fixed point. The determination of $\eta$ is related to the existence of an
exact marginal operator, for which an explicit form is given. The results are
extended to the exact Wetterich RG equation for the one particle irreducible
action $\Gamma$ by a Legendre transformation. An alternative derivation of the
derivative expansion is described. An application to $\N=2$ supersymmetric
theories in three dimensions is described where if an IR fixed point exists
then $\eta$ is not small.
