Yes, if your legislative environment and HR department will let you fire someone without going through written warnings and improvement plans, I agree that sounds easier than inviting them to start looking for another job.
I think you're likely speaking from different societal/legal models of employment. Here in the states, when you're ready to fire someone, you fire them. Unless you're dealing with a union. Then there are 10 additional steps.
That's not necessarily true if you want to minimize your exposure to an employment discrimination suit - often, you would want to have evidence that you gave the employee in question ample opportunity to improve. E.g. it helps the employer's position if they have regular performance reviews and those reviews reflect inadequate performance.
