Automated Memory Management in Lisp eliminates a major source of programming errors and a major drain on programmer productivity. For very large applications, it can also improve performance.
Computers are bad at creative thinking and good at bookkepping.
Very early computers forced programmers to code their own arithmetic operations, assigning specific bits to specific register and other locations. Assembly langage programmers have to code their own function call mechanisms and variable storage, carefully keeping track of where things are in memory. PC programmers sometimes had to manage paging between different memory areas or to disk, due to a lack of automated virtual memory management by the operating system. Automatic memory management for computer languages takes the next logical step. As far as the programmer is concerned, each piece of data created during execution of the program is always available.