No, you are not risking your rig by using the turboboost. Turboboost kicks in when there is a demand, and for most other purposes the CPU clocks down to use less wattage. Still, aftermarket cooling is almost always better than the stock cooler and will estend the longevity of your system.
I have an i5-2500K processor, an Asus P8 z68-V/Gen3 mobo, and stock cooler master case fans and a stock heat sink.
It is my understanding that to overclock safely, I first need to get an aftermarket heat sink and fans.
I went into the bios on my motherboard and noticed that the default for turbo mode was set to 'auto' and the processor was running at 3.7 instead of the stock 3.3
Am I risking overheating by running it in auto? I assume that the default setting wouldn't be anything to intense, but I wanted to run it by the experts here first.
On the overclocking issue, if you want to push 4ghz + 24-7 overclocks and adjuct core voltages then it is advisable to get a requisite aftermarket cooler, the stock cooler is sufficient for stock clock performance including the turboboost feature.
On the turboboost it is passive and only operates when the extra kick is needed. It operates of 1 core, 2 core , 3 core and 4 core boosts, with 1 core operating at 3.7ghz and 4 core turboboost at 3.4ghz.