Joining computer to domain

HI

In my environment there are two domain parent and child domain, eg abc.contoso.net   abc= child domain and contoso is parent domain. All the users details are in child domain abc, so all the computer are joined to abc.contoso.net.

Now i want to know what will happen or draw backs of joining the computers to abc alone and not full abc.contoso.net

Please advise

Aamir

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