Firstly, moving to another country, culture and linguistic environment is a challenge – this is the sociological aspect. Secondly, if we look at the patterns of intra-EU mobility, we can see that it is mostly emigration from the periphery towards the core. What are the implications for the economy of the EU and its member states? – this is the economic aspect.
Last but not least, the Brexit referendum and especially the campaign preceding it has shown that intra-EU migration (i.e. ‘EU migrants’ in the UK) has evidently become a political issue as well. Since the four freedoms are declared to be indivisible by the European Commission and thus free movement of goods and services without the free movement of people is not possible for the UK after its withdrawal from the EU, this topic may well be one of those impeding the conclusion of an EU-UK exit deal in due time.