This looks like a set of notes that are mostly correct but encourage bad practices. I think it's because they author doesn't understand git and doesn't know what they are doing.

>A lightweight tag is simply a named pointer to a commit. You can always change it to point to another commit.

Umm, you can do this, but in general you should never rename tags. Occasionally a developer will tell me the tag they pushed is incorrect and I'll agree to remove it only if they promise not to re-create it. If you read the man page on git-tag it's clear why you should avoid doing this.

>A lovely little tip – don’t forget that branch names aren’t limited to a-z and 0-9. It can be quite nice to use / and . in names for fake namespacing

If you use '/' is branch names you can create path conflicts. I've seen it happen and it took me a day to debug and figure out. There is some code checking for path conflicts in the git source but it's not invoked via all code paths that create branches. I recommend against using slashes in branch names unless you know what you are doing.