HAVS is Hybrid Adaptive Voltage Scaling. No matter what kernel you use, it will have a set minimum and maximum frequency. As load goes up and down, the frequency will go up and down (to save battery when not needed much, but provide performance when needed). This is the default behavior, but voltage supplied to the CPU is constant. With HAVS, the voltage supplied to the CPU will go up and down as the frequency goes up and down. This is meant to save even more battery power by supplying as little voltage as possible when the frequency is low (screen off for example). On its own, it will not affect the frequency any different than default behavior. There are two things you need to take into account - Governor choice and setcpu profiles. The governor is what determines what to set the frequency at based on load. Most governors such as on-demand, conservative, etc. make their decisions based solely on load. Basically, as load goes up, so does the frequency. What you probably heard about was the smartass governor. It will automatically underclock (set the max frequency way lower) when the screen turns off, and is designed to choose frequencies based on other factors such as battery life, etc. in addition to load. If you don't use the smartass governor, you can get the same effect by using setcpu profiles. A screen-off profile can be used to underclock when the screen is off. You should not use the smartass governor and setcpu profiles at the same time; they will conflict. You also don't need to be using HAVS to use either setcpu profiles or the smartass governor. They are two different things that are set for different purposes.
As to your other question, if you just want to see the frequency, you can use OS Monitor. If you put it in root mode, you can even set the governor and change the frequency (overclock/underclock). It doesn't have any kind of profiles like setcpu, though. It's free, though.