Cherry picking commits is generally best for when you have a lot of changes and you need only some of those changes to move over. Merging branches is the standard approach for when you want to develop some changes and then update a second environment with the "verified stable" changes. From your description, it sounds like merging branches is what you would want to use.
Just to be certain, let me be more specific. It sounds like you do the following:
Now currently, you find all the commits that were added to the `lab` branch and `git cherry-pick` them into the `field` branch. I assume you do this because, at some point in the past, you did `git merge` and either clobbered the slight code changes for the field or dealt with some merge conflict when things changed in both places?
To be clear, both approaches work. But `git merge` is easier especially when there are no merge conflicts. You can significantly reduce the chance of merge conflicts if you extract the code differences into different files. For example, you could use a different configuration file in the field versus in the lab. Or you could load different code based on whether a certain environment variable existed (like `__LAB_ENVIRONMENT=1`).
This allows you to use the much simpler `git merge` process and still not have to deal with merge conflicts nearly as much.
Let us know if you have more questions.
No, a branch that is merged does not cease to exist. You're merging the commits from branch X into branch Y, essentially (in the common case) making branch X and branch Y equivalent. It is quite common though for this process to be used:
In this example, you could replace `lab` with `development` and `field` with `production` to perhaps get a better idea of how this process works. You do some work and every so often, when the changes are ready, you merge the changes to "production" to deploy them. This is a simplified version of how we do work at GitHub to make bunches of changes to the github.com website each and every day.
Let me know if you have more questions.