We noticed a trend: students who pick a UI framework like Bootstrap or Material UI get off the ground quickly and make rapid progress in the first few days. But as time goes on, they get bogged down. The daylight grows between what they need, and what the component library provides. And they wind up spending so much time trying to bend the components into the right shape.
I remember one student spent a whole afternoon trying to modify the masthead from a CSS framework to support their navigation. In the end, they decided to scrap the third-party component, and they built an alternative themselves in 10 minutes.
This tracks with my experience. These kinds of frameworks don’t save time; they defer it.
The one situation where that works well, as Josh also points out, is prototyping.
If the goal is to quickly get something up and running, and you don’t need the UI to be 100% professional, I do think it can be a bit of a time-saver to quickly drop in a bunch of third-party components.