So my favorite size is actually 65%, and really the main difference between that and a 60% board is the arrow keys. Some people prefer to create a layer so they can use the arrow keys by holding a function key and pressing alphanumeric keys. If you like that (you end up saving a lot of back-and-forth movement of your right hand), or you spend most of your time using programs that don't require arrow-key input, you'll never miss them.
The rest of what you're giving up:
- Function keys
- I can't think of any common functions (at least from the programs and operating systems I use) that you'd use function keys for that you can't achieve equivalently using other shortcuts. Example: "F5" is a synonym for "refresh", but you can also just hit "Ctrl + R" in any Chromium browser. In rare cases when you need to use function keys, it's not that bad to just press, say "Fn + 7" than pressing "F7".
- Ins/Del/Home/End/pgup/pgdn
- You can either use alternatives or you can access these keys with a layer.
- Numpad
- Why do you need this? Are you unable to touch type the number keys above the letters? Are you a data entry clerk at a temp agency?
What you gain:
- Less of a reach to your mouse/trackball/touchpad/other input device and more room to move it around (if that's a mouse or something)
- Easier to set up multiple workstations (by workstation I just mean a monitor + keyboard + mouse) in a small area if you're into that. It's much harder when you're working with a full-size keyboard that's wider than your monitor.
- Force yourself to learn the ergonomic way of doing day-to-day tasks (ex: using ctrl + F to refresh webpage, using ctrl+n/p/f/b in emacs instead of arrow keys)
- Can (reasonably) position your keyboard so the center of the keyboard is in line with the center of your monitor. That way you aren't reaching way to the left/right just to type.
Is this a joke or was your friend joking with you? That wouldn't really be a reason to get a 60% keyboard because the keys/spacing are always going to be the same size. If you have small hands, you could effectively achieve the same thing as owning a 60% board by boycotting the number pad and function row.