How negatively do lowering blocks effect handling?

[Vicinity]

I found an awesome price for Hotchkis Drop Leafs (1.5 inch), but I'm thinking I might need to use a .5 to 1 inch worth of lowering blocks to get the fender just above the wheel. My current leafs have the rear all jacked up.

Will the lowering blocks effect the handling tremendously? Or even noticeably? My Brother was telling me about them, but it just seems kind of iffy to me.