N refers to new window:
Command-N：New Window
Shift-Command-N：Reopen the last window you closed
T refers to new tab:
Command-T: New Tab
Shift-Command-T：Reopen the last tab you closed
W refers to Withdraw:
Command-W: Close the active tab.
Shift-Command-W: Close Window
I thought W referred to Window…and often closed tabs and windows unintentionally…