Using multiple databases with helper files

[eluser]ryan656[/eluser]
Maybe I'm missing the point of helpers and models - why is it bad to have some helper functions that query the db? For instance, one of the functions in my login helper takes the username and password and checks the db for the user, should this function be in a model or should just the query call be in a model or what? The function also sets session information if the user is found, does this belong in the model as well?

I guess im asking..does every function that performs CRUD on a database belong in a model? And is it the whole function or just the part that performs the query?

Thanks,
Ryan