So i was looking up diffraction limits and i noticed that on my crop body, 60D the diffraction limit is f/6.9.
What does this mean in practical terms? If a lens i have is sharpest between f/8-f/11 should i still keep the aperture greater than f/6.9 because of this limit?
Diffraction is a property of lenses, not sensors as your title suggests. Therefore, a 60D does not have a diffraction limit.
Resolution of a lens depends on the lens design, and will be highest at different apertures for different lenses. However, having a high resolution is only one part of a high IQ. As you stop down, most lenses have reduced distortion, and reduced CA's.
Where a sensor comes in, is that sensors with more resolution can see diffraction better, but it is caused by the lens.
As you can see in this chart with a 15mp Canon 50D and 40mm f/2.8 lens, the resolution does not vary greatly out to f/8. The Chart below it shows basically the same pattern for the 5D MK II 40mm on 50D 40mm on 5D Mark II
Now, here is the Canon EF 100mm f/2.8 USM Macro lens. It shows the effects of diffraction really taking hold at f/16 and f/22. 100mm on 50D