Expandability should be concern while designing a PC. For certain systems, expandability is not that important. You design the system for a specific work, install the parts required to get the work done, and it’s done. For many general-purpose systems expandability is essential. For instance, if you want more storage space, you might want to add an additional HDD in place of replacing the original one. It can only be achieved if there’s a vacant HDD bay. Same way, embedded video might be sufficient enough, but if wants faster video than. If your motherboard has no AGP slot, the only alternative is to change the motherboard.

Do consider expandability while selecting parts to avoid disaster. Go for a case that has lots of room for growth. Select a power supply that has enough space to support additional drives, memory, and a faster processor. Select a motherboard that offers sufficient expansion slots and memory sockets for possible future additions. Don’t use less flexible parts unless you are sure that you’ll never be required to expand the again.