A question often asked is how do UK citizens do better in the EU as expats than UK expats elsewhere in the world.
UK citizens enjoy a considerable number of individual rights within the EU. The primary one being the right to work anywhere within the EU without the need for a work permit. Travel within the EU for periods of 3 months or less is open to all and there is a right to live as a non-working person anywhere in the rest of the EU provided you can support yourself and provide health cover.
There is a right of permanent residency (not naturalisation) in an EU country after 5 years. There are other regulations concerning aspects of being an EU citizen which facilitate moving around within the EU.
These rights don’t exist or exist to a much more limited extent if you are moving to most other countries in the world.
If a Brexit were to happen then these rights would probably be limited/reduced in some way or another, particularly if the UK imposed immigration restrictions on people from some or all EU countries.
Post-Brexit the situation will be different for those who have already taken advantage of the freedoms/rights by living/working elsewhere in the EU and those who have not done so.