Being able to create code with code, allows you to do away with boilerplate code. E.g. if you got a lot of code with just minor differences, you can make those differences into parameters in a macro which makes each of these code chunks.
That can be utilized both at high level and low level. GOAL is a cool example: https://en.wikipedia.org/wiki/Game_Oriented_Assembly_Lisp. Basically you can express assembly code in LISP syntax and then you can create higher level constructs like if, while, for etc statements as macros composing these lower lever assembly instructions. Because data and code is the same in LISP that allowed Naughty Dog when they used GOAL on the Playstation 2, to swap chunks of code in and out of memory as needed easily to maintain larger levels than the competition. It is also something that allows you to change a running system. I believe there was a case of a malfunctioning satellite running LISP code, which was debugged and fixed while it was running. Shutting it down for fixing was not an option.
I would also add another benefit of only using parenthesis. It makes it really easy to make powerful tools for LISP. Have a look at s-expression based editing. Instead of working line by line, or word by word as we are used to with editors, these work with whole blocks of code at the time. Normal editor commands involve jumping word by word or line by line. with LISP editors you can view the code as a tree with keyboard commands for jumping between tree siblings, up to a parent or down to a child. Instead of selecting x number of lines or words, you can select a whole subtree and delete it, move it, duplicate it or whatever. I think they usually call it paredit. Here is an animated demonstration of how it works: http://danmidwood.com/content/2014/11/21/animated-paredit.ht...
Disclaimer: I never really got used to LISP myself. I think it is cool, but it was too big of a jump for me when I started from C++ background. However I feel more used to it now as I've programmed a lot in Julia which is LISP like but with more normal syntax. Also when I first checked out LISP I didn't understand the need to change the way you think about navigating and editing code. If you edit the way you edit normal code I think it easily gets confusing. You lose track of the parenthesis. I didn't know about stuff like paredit then.
That can be utilized both at high level and low level. GOAL is a cool example: https://en.wikipedia.org/wiki/Game_Oriented_Assembly_Lisp. Basically you can express assembly code in LISP syntax and then you can create higher level constructs like if, while, for etc statements as macros composing these lower lever assembly instructions. Because data and code is the same in LISP that allowed Naughty Dog when they used GOAL on the Playstation 2, to swap chunks of code in and out of memory as needed easily to maintain larger levels than the competition. It is also something that allows you to change a running system. I believe there was a case of a malfunctioning satellite running LISP code, which was debugged and fixed while it was running. Shutting it down for fixing was not an option.
I would also add another benefit of only using parenthesis. It makes it really easy to make powerful tools for LISP. Have a look at s-expression based editing. Instead of working line by line, or word by word as we are used to with editors, these work with whole blocks of code at the time. Normal editor commands involve jumping word by word or line by line. with LISP editors you can view the code as a tree with keyboard commands for jumping between tree siblings, up to a parent or down to a child. Instead of selecting x number of lines or words, you can select a whole subtree and delete it, move it, duplicate it or whatever. I think they usually call it paredit. Here is an animated demonstration of how it works: http://danmidwood.com/content/2014/11/21/animated-paredit.ht...
Disclaimer: I never really got used to LISP myself. I think it is cool, but it was too big of a jump for me when I started from C++ background. However I feel more used to it now as I've programmed a lot in Julia which is LISP like but with more normal syntax. Also when I first checked out LISP I didn't understand the need to change the way you think about navigating and editing code. If you edit the way you edit normal code I think it easily gets confusing. You lose track of the parenthesis. I didn't know about stuff like paredit then.