Sublime is provided as freeware to a certain degree. If you want nightly builds, and the ability to get support from the developer to incorporate your requests into Sublime, then you would need to purchase a license for it. The beta builds of Sublime are usually not far behind the licensed version, so there's really no point in buying a license for it unless you want to use it without breaking usage terms, need the support, nightly builds, or the dialog is just simply annoying.

Note that if you have already decided you are going to use it, and have moved from evaluating it to using it, then you've broken the usage terms. It is likely to be illegal or at least unethical.