There are differences of opinion about the commercial facility. As Nag says, you can make a substantial income from it, but is this at the expense of your cars speed?
If you have your sponsors correctly positioned you should have more money coming in than you can spend. This also means that you can have the maximum number of staff replacing parts on the car & designing new parts.
As is so often the way with this wonderful game, there is more than one way to be successful.
Everything Edwin says is correct.
However commerce is also very useful for getting you out of debt.
It is good for keeping your income up if you are in a league that is too strong fo you and you aren't winning any money.
