Overview

Memory and disk space is getting cheaper all the time, but the cost of an hours development is increasing.  Often I see people trying to save memory or disk space which literally wasn't worth worrying about.

I have a tendancy to do this myself, because I can, not because it is good use of my time. ;)

Costs for comparison

Cheap memory - You can buy 16 GB of memory for £28.
Expensive memory - You can buy 1 GB in a phone for £320. (The entire cost of the phone)
Cheap disk space - You can buy 3 TB of disk for £120
Expensive disk space - You can buy 1 TB of the fastest RAID-1 PCI SDD for £2000.
The living wage in London is £8.55.

You might say that at my company, the hard ware is 10x more expensive, but it also likely you time is costing the company about the same more. 

In any case, this article attempts to demonstate that there is a tipping point where it no longer makes sense to spend time saving memory, or even thinking about it.

time spent	cheap memory	expensive memory	cheap disk	expensive disk
a screen refresh 20 ms	27 KB	150 bytes	1 MB	24 KB
one trivial change ~1 sec	1.4 MB	7.6 KB	60 MB	1.2 MB
one command ~5 sec	7 MB	50 KB	400 MB	6 MB
a line of code ~1 min	84 MB	460 KB	3,600 MB	72 MB
a small change ~20 min	1600 MB	9 MB	72,000 MB	1.4 GB
a significant change ~1 day	40 GB	0.2 GB	1,700 GB	35 GB
a major change ~2 weeks	390 GB	2 GB	17,000 GB	340 GB

Your mileage may vary, but just today some one asked how to save a few bytes by passing short instead of int as method arguments (Java doesn't save any memory if you do) Even if it did save as much as it might, the time taken to ask the question, let alone implement and test it, could have been worth 10,000,000 times the cost of memory it could have saved. 

In short; don't fall into the trap of a mind boggling imbalance of scale.