docs, Setting Up page, explain why the cargo installs are pinned?

Following [Setting Up page](https://docs.rust-embedded.org/discovery/microbit/03-setup/index.html), the tools versions are specified in _pinned fashion.._
Example: 

```
...
$ cargo install cargo-binutils --vers 0.3.3

$ cargo size --version
cargo-size 0.3.3
```

Are these pins required, and if so: for what reason? the latest version is .3.6 for example.