As in "if you can import your cheaply sourced products I can export my labour"
or as in "if you manufacture abroad, let me compete with that with moving my talent somewhere else"
or as in "freedom to sell my labour anywhere in the EU"
or as in "you can bring factories to my poorer country, but I can move to your richer country and also benefit"
or as in "part of the 4 freedoms that actually balance each other - they're not a set of 4 freedoms because of identitarian reasons, they exist because they're practical and work well together"
I am a migrant working in the UK and it's quite offensive that you would suggest FoM only lowers wages (HINT: It doesn't, look up the LSE's study about it), suggesting I'm here because I'm cheaper.