By "assault weapons" I'm assuming you really mean legal weapons like AR-15's, Mini-14's and such. Yes, they have benefits. They're accurate, you can reload less often, you can personalize it with any kind of attachments you'd like such as red dot sights, flashlights, laser sights, foregrips. Personally my AR-15 is a Colt. I've added a Troy quad rail, Magpul foregrip, Vortex Strikefire red dot sight, a mounted Surefire flashlight with two brightness settings, and a one point sling.
Assault weapons allow some people to defend themselves who wouldn't normally would not be able to. Although they are dangerous it can give people an sense of safety and allow them to go about their daily or nightly tasks without the worry of being attacked and having nothing to defend themselves with.
Like any other tool that exists the benefits of having one when you need it out weights not having when one when you need it. A list of benefits as it pertains to an AR15 as we know this is fire arm everyone is questioning.
Suitable for hunting
Recreational target shooting
Highly customizable ergonomics to fit an individual for safe and controlled use with out the need of a professional gun smith.
Easily repaired by the owner without the need of a gun smith
Easy disassembly in order to maintain safe reliable operation
It may confuse many why this is such a popular rifle when it comes to fire arms ... The simple answer is its a do it all rifle, the Swiss Army knife of rifles if you will and if someone can only afford one rifle this would be a no brainer choice.