Besides the direct performance issues already discussed, it is my opinion that:

1) A programmer who programs something of decent size and ceases to concern themselves with memory entirely will write code that will continue to bloat unneccesarily-so for the life of the software. At least some attention to memory is neccesary to keep usage reined in. You don't have to fight for KiB, but think about it. It rather seems to be a resource you can use 5% of, but without proper attention rapidly wind up consuming 100% of.

2) A programmer who disposes of the idea of using memory efficiently has probably discarded the idea of algorithmic efficiently in any way whatsoever. Pursuing memory optimization is a decent proxy for all forms of optimization.

[/not a programmer by trade]