It's been some years since I last used it, but some of the features are:
1) a repository of common (Chinese) software that you can install directly;
2) an alternative windows-update service that seems to work faster than windows's own;
3) a "janitor" tool, for inspecting and disabling auto-boot software, removing software otherwise tricky to remove, and removing temporary files;
4) a driver searching and matching tool that works much better than windows's own, which never worked for me.
I was a bit emotional in my last comment, since honestly, there has been some decent work that went into this software. They also started to integrate free antivirus software at some point, but I have heard a lot of bad things about it.
However, Qihoo 360 is notorious for spying on the user (there are some hard evidences), offering bogus functionality (placebo "optimizations"), taking advantage of the user in their "promotions" of other products from the company (a big, green, "install 360 browser now" button vs. a little, grey "no"), and cooperating with the authority on Internet censorship. It has become very unpopular among the tech-savvy people in China.
Absolutely nothing, it offers crap and it is crap. Just there is standard set every mainland chinese uses (if they're not expats), I often see QQ, PPStream (which at one point ran an open unauthenticated SOCKS? proxy to the world), 360 Antivirus/Suite (which is apparently awful), etc
when my friends want me to clean his/her computer(too many autostart programs and unnecessary softwares installed), I usually install 360 security. It is simply the easiest to use and do not have free equivalent. It may do some aggressive things, but that is the price if you want the good part.
Or you know... just use the in-built security in Windows 8.1. It's fun telling people they don't actually need to install a free AV anymore. They never believe you.
