While the usage of inline styles or code can accelerate development, given how easy they can be defined, it can lead to significant impacts in the long run. Having code scattered throughout the application instead of centralized in one place, compromises maintainability and reliability.
From the performance point-of-view, the usage of inline styles or scripts degrades performance as the page size increases. Also, the elements can't be cached unless the whole page is cached. The impact is greater with the inline scripts because the page rendering is halted while the inline code is interpreted.
Finally, and given the typical motivation behind using inline styles or scripts, they will probably be left undocumented, thus hindering code readability as well.