Here at the coast you never know when the winds will pick up. I use 5 gallon buckets that I fill with water, so they're about 35-40lbs each, at each corner. It's been windy before, but yesterday was easily 30-35mph gusts and I wasn't worried about the entire structure lifting up and flying away, but I began worrying about the structural frame twisting or buckling and then just completely falling apart and down on my display tables so that's why I removed the cover.
If I had tried to take the tent down during the gusty winds I was worried that would be when it would lift up and take off on me crashing into other vendors. A sturdier, higher quality tent will ease my mind and I won't worry about windy conditions again.