That would be my understanding too as it opens up a much larger character set but there are a number of caveats such as
On the user side: the ability to remember them and accurately enter them across different devices. This is much harder if you consider not using a password manager.
On the server side: The database needs to be able to handle storing them. Projects I've worked on using MySQL5.6 can't handle emojis but others using MySQL5.7 work with them just fine.