Many browsers cannot print framed pages appropriately. Of course, most browsers don't print anything really well, but at least regular pages normally print in full. With frames, it is common to have the print command result in the printing of a single frame. The original release of HTML was simple enough that many people learned it without any problems. Frames are another matter, though.
Frames are currently so hard to learn that many page authors write buggy code.
Search Problems Search engines have trouble with frames since they don't know what composites of frames to include as navigation units in their index. User Preferences Many websites that offer users a choice between regular and framed versions have found that most users prefer frame-free designs. The main issue in using frames is to ensure that URLs keep working. The destination frameset may well have many frames that are identical to the ones in the departure frameset and will be cached in the browser, but by forcing a complete reload in principle, the browser gets a new URL for the destination. For example, a very long directory or other alphabetical listing could have a frame on top listing the letters of the alphabet.