The waveform from a half wave rectifier looks just as it is described by its name: half of a full sine wave. That will cause a pulsed or "ripple" effect in the output voltage and current that come out from the rectifier.
Whether that will cause a problem depends on the application you are using.
For instance, if it is a light bulb, it will appear to flicker at the frequency of the alternating current service that has been rectified, which can be very annoying!
If it is a device such as a charger for the battery of a digital camera or an electric shaver, the pulsed output current doesn't matter at all.