The devices are derided sometimes for being limited in their reliance on apps, but those apps can allow a user to accomplish a myriad of tasks, from simpleword processing to completing business projects.
If you're absolutely certain you're going to run only text-based word processors or spreadsheets on an IBM-compatible, or simpleword processors and spreadsheets on a Mac, you can settle for a basic box with one megabyte of memory and a 40-megabyte hard drive.