Countries negotiate Free trade Agreements for a number of reasons:
By eliminating tariffs and some non-tariff barriers Free trade Agreement partners get easier market access into one another's markets. Countries negotiate FTA's for a number of reasons.
Exporters prefer Free trade Agreement's to multilateral trade liberalization because they get preferential treatment over non-Free trade Agreement member country competitors. For Instance in the case of ASEAN, ASEAN has a Free trade Agreement with India but not with Canada. ASEAN's custom duty on leather shoes is 20% but under the Free trade Agreements with India it reduced duties to zero. Now assuming other costs being equal, an Indian exporter, because of this duty preference, will be more competitive than a Canadian exporter of shoes. Secondly, Free trade Agreement's may also protect local exporters from losing out to foreign companies that might receive preferential treatment under other FTAs.
Possibility of increased foreign investment from outside the Free trade Agreement. Consider 2 countries A and B having a Free trade Agreement. Country A has a high tariff and large domestic market. The firms based in country C may decide to invest in country A to cater to A's domestic market. However, once A and B sign a Free trade Agreement and B offers a better business environment, C may decide to locate its plant in B to supply its products to A.
Such occurrences are not limited to tariffs alone but it is also true in the case of non-tariff measures. Especially when a Mutual Recognition Agreement (MRA) is reached between countries A and B. Some experts are of the view that slow progress in multilateral negotiations due to complexities arising from a large number of countries to reach a consensus on polarizing issues, may have provided the impetus for FTA's.