Question: > 
> Not Counting the OS And the requirements to run the Development software. The storage space required.
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Strictly speaking from work perspective(company setup and not freelancers).A individual developer ( not considering a build system) unless into areas of video,audio processing( huge raw files) 3d/graphics development.
How much storage space would be required.

* Even if we account for the software trials to download or reading material.is it Right or Safe to assume 20GB would most suffice and any thing more would be a waste and or would be improperly utilized?.
* What is the typical hard disk space allotted per developer in an office setup.This may differ per role or specific requirement and on what type of work the company is into. but on an average for a developer/programmer how much space is normally allotted.

Edit: 

**To Clarify Intent** 

These are questions i had faced by business/management people.I only wish to understand more in this regard to give an answer(or better answer)the next time i come across them. I am neither making assumptions or intend to give offense to any one in this regard.It would be helpful if some links to data online were provided in this regard.

Edit 2:

* The issue as i understand was restricting the storage space to only the saving of work files to discourage extraneous usage...
* Not about scrimping/cost saving on hardware.

Answer: 
Development needs a LOT of space.

We use VM images as units of configuration management for developer setups.

Once you've copied the VM onto your machine you start it, update the source code from the VCS and you're running. No futzing with developer setups.

Each VM image is about 20Gb. 4-5 of those. i.e. we generally need 100 to 120Gb Gb

Mind you, they are not "per user" on the machine things, only need one.
Sufficient that your developers don't have to worry about running out of space whilst working. In my case that's room for big checkouts, (sanitised) copies of databases, VMs and "other stuff" - although some of the other stuff ought to be on shared space (of which I'd need a lot) to avoid duplication in a team environment.

Use (abuse) of space on a work PC for extraneous purposes should be a matter of policy and one not of enforced physical limitions on their principal dev boxes - not least because developers are the kind of people who will be able to find creative ways round restrictions quite possibly to the detriment of your network as a whole.

Note also that this is one of those areas where developers and other users do actually need to receive different treatment.