For those who do not know, DRM is the technology that prevents users from taking copies of various types of videos, audio and even written material in electronic form. It is an abbreviation of Digital Rights Management – and its your rights they are managing. Instead of going into too much technical detail, I want to just list some of the effects. Obviously I am assuming that DRM will work, either because it technically effective, or because it is now a criminal offence to bypass it in most countries.

1. It Prevents expansion of the public domain. In the past, once a copyright expired, the work it covered would fall into the public domain. When the copyright expires on a work that is only distributed in a DRMed form, the DRM will contune to prevent legitimate copying.
2. It also makes it impossible to take back-up copies of works in case the original media are damaged or lost.
3. It frequently prevents consumers from enjoying their purchases because of a bug in the system. The pirated version is better because you know it will work.
4. It prevents inter-operability between different systems. Certain Nikon cameras, such as the D2X, encrypt part of the information in your photos so you can not read them fully without Nikon’s software.
5. It makes archiving difficult. Suppose you use software that encrypts your work, 20 years later you no longer have the original software, and it is no longer available. You now cannot view it.
6. It locks users into a particular system. If you buy works using a particular DRM system, you must have players or software that use the same system, you cannot switch without losing use of past purchases.
7. It can lock competition out of a market because each DRM system requires a central authority that controls it and decides who can make devices and software that use it.
8. It adds expenses that are passed on to consumers
9. It makes it difficult (or impossible) to create certain types of systems, such as a home media server – a computer that will allow you play music stored on it though other computers in the household.
10. It makes devices and software less reliable. Many DRM systems also have provisions for revocation: centrally shutting down systems that have been compromised. If you buy a Brand X player and it is discovered that someone else has broken the DRM on Brand X, then your player will stop working too.

A good detailed case study of the effects of DRM is this analysis of Windows Vista DRM. Microsoft’s attempts to rebut the allegations lead them into contraditions with their own documentation, which are discussed here.

A more general discussion can be found on FAQ section of the anti-DRM defective by design website.