Is Income Summary account always needed?

My teacher said when we do closing entries, we can choose the four steps, namely

Dr I/S
Cr Revenue

Dr Expenses
Cr I/S

Dr I/S
Cr Capital

Dr Capital
Cr Drawings


Or she said we can choose the three steps method by closing revenues and expenses right into the capital account. I was wondering if we can always close revenues and expense right into capital, what is the original purpose of having this temporary account, Income Summary? It's pretty much useless if that's the case.