After I enter T slips, TurboTax then asks me to enter Statement of Income. Why does it ask me for same information already entered in my T slips? This does reduce refund.

If you became a resident of Canada during the year, you will be asked for your World Income - the income you made outside of Canada before you became resident. While you won't be taxed on this income, it may be used to calculate credits or benefits. If your World Income + your Canadian income is too high, you may no longer be eligible for credits or benefits that are meant for lower incomes.