aromatase inhibitors can be used to prevent gyno and bloat. SERMs work by blocking the ER (at least in breast tissue), hence they can be beneficial in cases where there is cross reactivity or when there are offending xenoestrogen.
It is always good to have an AI and SERM on hand. During cycle unless problems present AI's are generally preferable, though adding a low (very low) dose serm can be quite beneficial to cholesterol and other health parameters.
to answer: AIFM alone is sufficient just as arimidex/letro/aromasin is sufficient. However for the reasons mentioned above having a SERM on hand is essential