Question: I would like to name my files and folders according to a specific date, e.g. `03.04.2016`.

I see I can use them but are there any disadvantages to using periods in files or folder names?

Answer: 
They are valid and you can use them but yes, there are disadvantages.

* A period is often used in regular expressions to represent a single character.
* A period in filenames is often used as the standard separator between filename and extensions.
* A period at the start of a filename is used to indicate configuration and/or hidden files.

For these reasons using periods in filenames for other purposes often leads to issues down the road with other command line functions and other tools and frameworks not expecting them and not working correctly.
Periods by themselves have no meaning, but what follows the period may have meaning to programs that look at the file suffix. For that, look at `/etc/mailcap` and `/etc/mime.types`

Some implementations of `ls` can sort by suffix as well, e.g.

```
ls -lX

```

for GNU coreutils.