#include <bits/stdc++.h> is a precompiled header implementation file.
Minimizing the inclusion is a smart approach from the standpoint of software engineering.
If you use bits/stdc++.h>, it includes a number of files that your programme may not need, increasing both compilation time and programme size needlessly.
However, in competitions, employing this file is a smart idea if you want to minimise the time spent on tasks, especially if your rank is time-sensitive.
It is compatible with the majority of online judges and programming contest venues, including ACM-ICPC (Sub-Regionals, Regionals, and World Finals) and many more online judges.
Its downsides are as follows:
1. lengthens the compiling time
2. Because it makes use of a non-standard internal header file of the GNU C++ library, it will not build with MSVC, XCode, or many other compilers.