Basically, they don't get the benefits of being in the European Economic Area if they are not in it. The EEA mainly provides the for the free movement of "goods, services, persons and capital" within the European Single Market, so the states which are not in the EEA will not have access to the single market.
However, EU member states are obliged to apply to be part of the EEA.
The benefits of being in the EEA are as follows:
All relevant Internal Market legislation is integrated into the EEA Agreement so that it applies throughout the whole of the EEA. The core of these rules relate to the free movement of goods, capital, services and persons. In addition, the EEA Agreement covers horizontal areas such as social policy, consumer protection, environment, company law and statistics. In order to ensure equal conditions of competition throughout the EEA, the EEA Agreement mirrors the competition and state aid rules of the EU Treaties. It also provides for participation in EU programmes such as those for research and education.
In Croatia's case, the agreement has transitional provisions, but it will formally enter into force only when all EU and EFTA members have ratified it.
The agreement also enables Norway to implement the transitional provisions included in the EU’s membership agreement with Croatia. Most notably, this applies restrictions on the free movement of workers from Croatia for the duration of the transition period, which may be up to 7 years.
The agreement will enter into force once formally ratified by EU Member States and the EEA/EFTA countries; Norway, Iceland and Lichtenstein. In Norway, the Storting will have to finally ratify the agreement.