The biggest difference is that you have a limited number of withdrawals from a savings account per month, where a checking account has unlimited withdrawals. (personalprofitability.com)
You need to add inflation (and investment return) because compounding interest will make a huge difference at time of withdrawal How do you save for your kids to go to college? (financialsamurai.com)
For example, in the payout schedule, you can enter additional withdrawal amounts to either add to or reduce the amount of a withdrawal for a specific period. (vertex42.com)