Migration generally, whether permanent or temporary, can often help alleviate problems in countries where the economy is under pressure. Poverty can be mitigated and the indirect impact on services such as health, might also benefit. However what these countries can also lose is a knowledge base of skilled and educated workers, and families on a social and personal level can also suffer particularly where children are left behind if the migration is temporary.

Where highly skilled workers move away, and particularly when the move is permanent, this might have a downward spiral effect. For instance, in cases where there is not enough work to support research, more researchers may leave the country than is desired and this can force further closures.

The public sector can suffer in a similar way, particularly when job cuts are made at managerial level and this forces a push factor away from the native country toward one with more opportunities. Again, the end result is that more job cuts are necessary because of the downward spiral.

These are just two examples of how migration of skilled workers can negatively impact the country of origin not just in the current climate but also into the future because the source of progression has been pushed away by economic necessity and pulled toward countries where opportunities are greater.

That's too generic a question as it can very much depend on the country and the nature of the migration. Reactive an circumstance/event driven migration does not always result in a brain drain for the country that the migrants are leaving.

Those that feel that they have less chance of progression in their home country - possibly because middle management roles and above are allocated through nepotistic, oligarical or corrupt processes can be a more significant loss.

Consideraton needs to be given too about whether the migration is of a temporary or permanent nature. Whilst a brain drain could be an issue there could also be a net gain for the migrant's country of origion if an equally trained or qualified person replaces the migrant from a perceived Economically weaker country

In my opinion, it impacts them a great deal. Countries of migrants' origins are usually the ones that are poor or where economy is declining so people with high education or wanted jobs migrate in wealthier countries leaving their homes. Every single expert which leaves a country where there is already not much experts, leaves a large loss for that country and its human capital. For a country that already lacks doctors, every next medic that leaves means prolonged waitlists in clinics, quality of service diminshed and public health in general affected. For every competent teacher leaving the state there are at least 100 potential students that won't be able to learn from him and maybe one day want to be him, and without education there is no progress in any field , so the only way is backwards, not progress.