There’s no doubt that domain accounts with weak passwords can be a serious concern for companies, there are a few ways you can protect yourself against issues like this. The first is to set a domain and local account lockout policy and the second is to enforce password complexity. However if your users are using “Password1” as their password, neither of these steps will protect you.
On a Penetration Test, once you’ve scored Domain Admin (DA) Access, it’s generally a good idea to take a look at the hashes stored in Active Directory (AD). Not least because it’ll point out all of the weak accounts that you missed on your journey to DA but also because password reuse across accounts may get you into other systems, such as Linux servers or the network infrastructure. There are a few methods of dumping hashes and every PenTester I expect knows one of these, but I’ve included a few as it’s always good to have a backup plan.