Checkout branch and prune everything related to previous checkout (incl. LFS remains)

[Mateusz Loskot <mateusz@loskot.net>]

Hi,

I have a repo of a superproject with number of submodules.
lots of files of both are in Git LFS.
The repo comes with multiple long-lived release branches.
The complete clone transfers 20 GB of Git and Git LFS objects.
Checkout of master deflates the total repo to 40 GB in total,
that is the objects and the working tree files together.


Let's consider three separate clones as canonical way to create
three working copies, one per the long-lived branch:

```
git clone --branch master      --recursive --jobs 8 https://repo repo_master
git clone --branch release/1.0 --recursive --jobs 8 https://repo repo_release1
git clone --branch release/2.0 --recursive --jobs 8 https://repo repo_release2

```

I'm trying to work out a network-optimised equivalent of the above:
- clone once with the default master checked out
- make multiple copies of the cloned repo
- checkout release branches

How to checkout an existing branch fetched from remote,
delete the previous branch and clean up any remains?

How to clean up everything related to the previously checked out
master and its working tree, any cached previous LFS downloads etc.?

But, to keep the history of origin/master.

Here is what I have come up with for the the network-optimised workflow:

```
git clone --branch master --recursive --jobs 8 https://repo repo_master

cp -a repo_master repo_release1
cp -a repo_master repo_release2

cd repo_release1
git checkout -b release/1.0 --track origin/release/1.0

git pull
git submodule update --init --recursive --jobs 8

git branch -D master

git lfs prune
git submodule foreach --recursive git lfs prune

git lfs checkout
git submodule foreach --recursive git lfs checkout
```

Does it look correct or any steps are missing/redundant?

Does it make sense to run any of these, at which point?

git gc --aggressive --prune=now
git submodule foreach --recursive git gc --aggressive --prune=now

Please, assume, no new commits will happen locally between the
`git clone --branch master ...` and `cp -a repo_master ...`.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net