People hear that a line of credit charges "simple interest" while a mortgage is "amortized" and conclude one of them must be hiding something. Neither is. Both charge interest on what you owe. The real differences are how often they look at the balance and how the payment is structured, and those two details are what this entire strategy leans on.
Your mortgage checks the balance once per cycle and charges a month of interest on it. Pay on the 1st or the 28th, same interest either way. The payment itself is fixed by an amortization schedule, which is just a formula that levels the payment over thirty years. Early on the balance is huge, so most of that level payment goes to interest. That's the front-loading people complain about, and I unpacked it in Why Your Early Mortgage Payments Barely Touch the Principal.
Your line checks the balance every single day. Owe less on Tuesday and Tuesday costs you less. That daily attention is what paycheck parking exploits. Income lands in the line and starts lowering the interest clock immediately, even if the money leaves again for bills in two weeks. On a mortgage, that same two-week visit would accomplish nothing at all.
One caveat so nobody oversells this to you: daily interest cuts both ways. Carry a high balance on the line and it charges you daily too, often at a higher rate than the mortgage. The daily math only works in your favor when cash flow through the line is strong and the balance trends down. It punishes a stagnant balance just as efficiently as it rewards a shrinking one.
So the pairing is deliberate. Amortized debt is cheap but rigid. The line is flexible but pricier. Route your cash flow through the flexible one, aim chunks at the rigid one, and each tool spends its life doing the thing it's actually built for. The complete sequence is laid out on the How It Works page.