Jim, you can use them for both!
I personally have one installed in my WRX. I use it everyday, as well as for autocross.
It keeps you planted in you seat for the twisty bits and on a long drive can easily be adjusted to keep you in your seat without felling restricted.
It gives you 80 % of the holding power of a racing harness, without the hassle of installing a racing harness. More importantly, living with a racing harness day to day can be a chore. The CG Lock requires no drilling or modification to install. Not to mention that the CG Lock is half the cost of less expensive harnesses.
The CG Lock is SCCA National Solo rules compliant.