Adobe Lightroom 3 (LR3) Lens Corrections

Under the Lens Corrections tab within the Develop module in LR3 there is an option (check-box) to Enable Profile Corrections.

I shoot with a Canon 5D Mark II and a 7D with various L lenses.

Is there a scenario where I would -not- want to enable lens corrections?

If not how do I turn that feature on by default?

The lens corrections are very memory and CPU intensive and many many people with computers that are less than super whiz-bangs have found that when using the local adjustment brush, spot removal tool or graduated density filter after the lens correction has been enabled, those tools really drag their butts. The solution is to leave the L.C. until the last step in the workflow.

If you don't have that problem, you can reset your defaults to include L.C. (Alt/Opt and the Reset button changes to Set Defaults) or you can create a preset.