Ensuring your project remains relevant in the future!
provides a breakdown of the changes from Bootstrap 3 to 4 in code format, it's worth checking out.
There have been several notable changes in:
- Browser support
- Global changes
- Components
- Miscellaneous
These changes are detailed in this link, and it reinforces the fact that:
Bootstrap 4 represents a significant overhaul of the entire project.
While it's not imperative to upgrade immediately, there are exciting developments in bootstrap-4. The choice is yours - stick with what works for now or future-proof your app a bit. The decision is yours to make!