It’s pretty unlikely you need to pay for a full copy sandbox.
Not impossible, or maybe it would be better to say, “Not never.” But most of the time it would be an expense you don’t get value from.
Don’t get me wrong: I think sandboxes are terrific. (One post already about them. More planned.) You should make it your practice to use them, particularly for building and testing new functionality.
Enterprise Edition’s sandbox allocation is 25 developer sandboxes, one developer pro sandbox, and one partial copy sandbox. That’s likely to be more than you will ever need.
Access to a full copy sandbox is something that AEs suggest because they’ll make a fat commission on the sale. Even more, they use access to a full copy sandbox to try to sell you Unlimited Edition (which you definitely don’t need).
You can purchase a full copy sandbox a la carte. According to the Salesforce.org pricing sheet, a full copy sandbox costs 30% of the net licensing cost of your org.
[Side note: It’s not easy to find that pricing sheet on the Salesforce.org section of the website. Despite years of community clamor for transparency in pricing, I still point you toward the Crowdsourced Salesforce.org Pricing Guide, which I have written about before.]
For the purposes of that calculation, your free licenses count at their normal price ($495), not as zero dollars. So that means the minimum cost of a full copy sandbox is $1,485. It could easily go up from there. (For example, on new Nonprofit Cloud, instead of NPSP, your first ten licenses are each worth $720...)
A full copy sandbox is an interesting tool. At the moment you spin up a new full copy sandbox it’s literally a clone of your production environment, metadata, data, and all. It even has the same record Ids for things. And it’s large enough to have everything, even if you have absurd amounts of data.
So large organizations need a full copy sandbox when they want to test new development against sufficiently large datasets or even testing new integrations and how they will work with all your data.
Plus full copy sandboxes are often helpful in the context of a migration project.
Keep in mind, though, that full copy sandboxes can only be refreshed every 30 days. So you have to plan your strategy carefully. These are not as flexible as developer sandboxes.
When to Use One
Full copy sandboxes have use cases, so I’m not 100% saying you don’t need one.
But you only need one if you have plans for it. Examples:
A nonprofit that is consolidating two orgs down to one but one is remaining live. Having the full copy sandbox allows you to work on the consolidation project against the full data volume.
A two-phased project where you need that full copy to run automation load testing, etc. You complete Phase 1, then spin up the full copy, then all Phase 2 work can be tested against real data volumes.
I suppose you could also use a full copy sandbox as a poor substitute for a backup and restore tool. As long as you remember to do it, you could refresh every 30 days and have a monthly backup copy of all your data. The weekly export gives you four times more frequent backup and automatically runs. Plus restoring, if you found a problem, would be quite painful from a partial sandbox similarly to the weekly backup. So I don’t actually recommend this. But I suppose you could use a full copy sandbox this way.
Why You Don’t Need One All The Time
If you have a project in the works that is going to take advantage of a full copy sandbox, Salesforce’s AEs will be more than happy to sell you one at any time. You’ll be able to add it to your contract mid-year at a pro-rated price. (And then you should ask to have it removed when your contract renewal comes around again!) If your project timing crosses your contract year, you may end up paying for a year and change (because you can’t lower your contract mid-year), but it’s not something you need in perpetuity. Only pay for it when you’re going to use it.
[As I said: Unless you’re a really large org.If you have multiple consultants plus a lot of internal folks doing development, maybe you do need a full sandbox. Maybe you’re even of the size that you need UE and, therefore, get one as part of that edition. But that’s just not that many organizations.]
Poor Man’s Full Copy
If you put a little effort into it, and your org isn’t too large, you can make a partial copy sandbox serve as a very credible stand-in for a full copy. When spun up, partial copy sandboxes also have record Ids that match production. And they can hold 5GB of data, which is quite a lot. So if you build a sandbox template that is broad enough to bring in all your records, you’ll effectively have a full copy. For free!
Plus partials can be refreshed every 5 days, so you can iterate on testing more quickly. I think partial sandboxes are pretty handy. I’ve done testing for two household account migrations without ever looking for access to a full copy sandbox. (In fact, I did most of the testing work for both of those using developer sandboxes that I filled with real data using CumulusCI’s data loading powers.)
Again, unless you’re a huge org or have a specific project with specific kinds of data or volume needs, you can probably do anything you need in a partial copy sandbox.
You only need a full copy sandbox when you have plans to use it. Don’t pay for it when it will sit untouched.