Explanation
With a Standard subscription plan, you can add multiple products to your existing site, such as Jira Service Management1. You can also add Jira Software to a new site, if you need to create a separate instance for a different team or project2. However, you cannot create or use sandboxes, which are only available for Premium and Enterprise plans3. You also cannot change release tracks, which are only available for Enterprise plans4.
References: Manage your bill for Standard and Premium plans, Add a new product to your organization, How many instances of a product does my organization need?, Manage product sandboxes, Release tracks for cloud products