Putting aside the tax is a good idea and allows you to pay your Corporation Tax early (in the UK you have 9 months from the end of your company year to settle). Why would you do that rather than hang on to it? Well, just as the authorities will charge interest on late payments, so they will pay it on early settlement, and at a reasonable rate. So not only do you get peace of mind at having paid the bill, you can also look forward to a small reward once the due date has passed.