The employee who serves as an internal consultant may not have greater consistency in their work than other employees in the company but they will have more than consultants who work in every other model.
Employee Benefits (Vacation/Sick Leave, Holidays, Health Insurance)
Model I and Model II consultants will have all of the standard employee benefits that most Americans expect. All other Models do not offer the same level of benefit and may not offer any at all.
Tax Benefit (employer pays half of Social Security and Medicare)
In the US, employees and their employers share the burden to pay fees to the government to cover Social Security and Medicare. This benefit may seem invisible to people who work as an employee of a company but it becomes apparent when they no longer work as an employee.
Employees generally avoid being taxed in multiple states for income tax.
In my experience, people who work as an internal consultant may travel quite a bit in their work but they will be taxed in a single location.
Potential for support for books and tuition support for both formal and professional education
Model I consultants are likely to have many different educational benefits. They get support for ongoing professional education through college courses and seminars. Companies pay to help employees to stay current in terms of technology.
Promotion opportunities within the company
The nature of the work of an internal consultant means that they will meet many different people within the company. This gives them the opportunity to build a large network of professional contacts within the company. Since they will also have training in the latest technology. they will be ideal candidates for promotions.
Lower accounting burden than in some other Models (expense Reports, State & Federal Income Tax)