While by no means an “essential” setting for many users, the internalBorder setting in rxvt-unicode can go a long way towards making the terminal more readable or simply looking more the way you want. It adds some padding between the edge of the terminal window and the start of the text, both at the top/bottom and the left/right of the window. This is especially useful if you use a tiling window manager and do not otherwise have spacing between windows.
The (arguably) venerable xterm terminal emulator has a similar property called BorderWidth.