An acoustic piano can last 100 years or more, while a digital piano may be obsolete in 5 years. An outdated keyboard is often difficult to sell. The tone and touch of an acoustic piano is usually far superior to a digital piano and it will hold it’s value much better than a keyboard. The disadvantages are the size, the cost and the tuning expense.
The keyboard has made it possible for many students to learn to play the piano. The advantages of a keyboard are the lower cost, smaller size, ability to play quietly with headsets and no need to get tunings. Most digital pianos have a MIDI output which allows you to connect them to a computer via an inexpensive interface, which allows you to record and edit your playing and add additional parts, as well as control other instruments. Many times, a student will start lessons with a cheaper keyboard and when the parents see the level of commitment that the student has to learn to play well, they will then go and buy a much nicer keyboard or an acoustic piano.