Your spouse or common-law partner's net income is the amount on line 23600 of their return, or the amount that it would be if they filed a return. Even if you are not claiming a spouse or common-law partner amount, the CRA requires you to provide this information.
TurboTax uses this amount to calculate federal and provincial tax credits, including the spouse or common-law partner amount, CCB, GST/HST credit, pension amounts, etc. It is also used to determine which spouse is eligible to claim child care expenses.
If you are preparing a coupled return, this amount is transferred automatically to your return when you enter your spouse or common-law partner's T-slip information.