Short answer: Savings reduce loan balance for interest calculation. Pay interest on net amount. Access to savings remains.
Your savings account is linked to your mortgage. The bank only charges interest on the difference. If you owe $400,000 and have $50,000 savings, you pay interest on $350,000. You still have access to your savings. It saves more interest than a savings account pays. But the mortgage rate is usually slightly higher.
Loan: $400,000
Savings: $50,000
Net Balance: $350,000
Interest Saved: ~$3,500/year
Vs Savings Account: Savings account pays ~$2,000/year