A computer that is expandable will allow you to add more storage space, memory, and other peripherals. This prevents you from having to purchase up front what you are not convinced you will use immediately or at all. Expandability will guard against your computer becoming obsolete too quickly. You have to plan to be careful with your computer. If it is portable, you have to be particularly careful.
Computers are valuable, typically more valuable than stereos.
You must be on your guard against theft. It is important to treat the data on your disks as a valuable commodity that needs to be protected. This takes some time, but it is worth the effort to avoid the disaster of losing your work. Most computers today are very reliable. If you are willing to take a risk and are able to replace parts on your computer yourself, you can save money and learn more about your machine.