Why does FormT2125 take your negative income from expenses and increases the amount of your return.

[TurboTaxKim]

When you enter your Self-Employment expenses, they are reducing your income from that business (possibly even creating a loss) and this, in turn, results in a lower taxable and net income.

If your business is in a loss situation (expenses exceed income) this will apply against any other income you may have, lowering your tax payable and resulting in a larger refund.