I assume that in large projects where you want to use every function that the css framework provides, you should go for it. If on small sites, using Bootstrap / Foundation will be a factor in slowing down.
Otherwise, if you are confident that you are creating an adaptive environment yourself, you should go forward. But, if you feel that you are not accepting help from others in the form of css frameworks.
This question is too broad and there may be many possible answers. The above is just my point of view.
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