An electric piano or keyboard is often used by children starting to learn piano who are not yet ready to commit to buying an acoustic piano.
For pure beginners of a young age, an electric instrument would be an interesting alternative at the start. Being able to play with the sound buttons, rhythm box and other functions on a electronic piano is quite engaging for a young child. These instruments do not require tuning and may be less 'noisy' as their volume can be turned down.
Long term disadvantages
Electric keyboards may distract from learning the subtleties of tone and touch needed to play well on an acoustic piano. Personally, I find it best to switch to a real piano after half a year to one year to allow good development of technique and listening skills. Or better yet, just start with an acoustic instrument.
When learning classical music, acoustic pianos are highly preferred. Tonal and touch sensitivities and a good acoustic piano really cannot be compared to an electric piano.
Acoustic pianos are the regular wooden ones that you see. There are hammers and strings inside and sound production is basically mechanical: when your finger hits the key, the hammer inside hits the string and produces the sound.
Electric keyboards produce sound by electromagnetic means and are really altogether a very different instrument.
Acoustic instruments are often heavier in touch compared to electric ones and are far more responsive. Electronic ones tend to be lighter in touch and limited in their responsiveness.
Even touch-sensitive electric keyboards or pianos are often limited in tonal range and quality compared to their acoustic counterparts. Developing a sensitive ear is therefore not easy.
This is a rather new type of piano for those who prefer to have a quiet instrument. This piano offers all the traditional acoustic qualities with the option of lowering the volume or using headphones.
In some silent pianos, you can pull a lever or depress a middle pedal to prevent hammer heads from hitting the strings to enjoy some quiet time.
This would also be a good buy offering the best of both worlds.