I have been using *Mathematica* for about 2 years and I'm pretty ok to write and optimize my code. Wanting to improve my practice, I often look at code examples. However, I can not determine if there is a "good way to do" with the use of functions `Clear`, `ClearAll` and other related functions (as `Remove`). I note that several people clear all at the beginning of each code, while other clear only the variables. So what would be a good practice?