A stand mixer basically mixes anything that a normal hand mixer does. However, a stand mixer allows you to blend, mix, combine, and whip your ingredients for longer periods without tiring.
You can definitely do more with a stand mixer because of the higher mixing power and special attachments that come with it. Due to the high wattage, stand mixers are more costly. The only setback, though is that a hand mixer is more portable than a stand mixer.
You don’t necessarily need a hand mixer if you already invested in a stand mixer since they are one and the same thing. The difference vividly shows itself in terms of storage, power of control, portability, and cleaning.