There is a big difference between allowing an uncomfortable emotion to show up as apposed to tolerating that emotion. Tolerating implies some mild resistance to the emotion and putting up with it. However allowing implies some level of acceptance of the feeling and a letting go of it. Once we can allow uncomfortable emotions to arise in our lives we find that they subside much quicker and this allows us greater perspective and a reduces our base line of stress.
I know in my own practice i have spent a long time tolerating negative emotions but i have only recently began to fully allow and accept them. the difference is huge.