Every computer regardless of purpose requires storage for all files and data swaps. Hard Drives come in all sizes though usually increments of 20 gigabytes. All programs, documents, images even browsing history require a certain amount of hard drive space.
Hard drives come in all sizes from 20GB to over 1,000GB (or 1TB) the size should be decided upon by the need of the computer and the tasks at hand. The largest concern of a hard drive is having too little storage for all of the programs and user saved data.