Determining an appropriate license can be complicated and should be informed by needs, copyright eligibility, institutional intellectual property policies, and applicable intellectual property and copyright laws.
Why license in the first place? In many jurisdictions (including the US) intellectual property rights vest in the author of a creative work whether they assert it or not. Also, in most jurisdictions (including the US) the rights one has for work copyrighted by someone else is limited to fair use. A license grant more rights than to a user than they would otherwise have.
By publishing a research product, as a scholar one usually intends to benefit from that by allowing the product to have a wider impact. Not stating any licene or terms of reuse is effectively in contradiction to that.
What is an open license? What constitutes an Open License is well defined: the Open Definition lays out very clearly the basic rights that any Open License needs to grant. Particularly noteworthy for scientists, the definition does not allow to discriminate between academic and commercial reuse.
Choose a standard license (such as an OSI-approved license for software, a Creative Commons license for other creative works, and a Public Domain Waiver for data) instead of using or creating a bespoke one.
References and URLs
Morin A, Urban J, Sliz P. A Quick Guide to Software Licensing for the Scientist-Programmer. Lewitter F, editor. PLoS Comput Biol. 2012;8: e1002598. doi:10.1371/journal.pcbi.1002598
Carroll MW. Sharing Research Data and Intellectual Property Law: A Primer. PLoS Biol. 2015;13: e1002235. doi:10.1371/journal.pbio.1002235
Patterson DJ, Egloff W, Agosti D, Eades D, Franz N, Hagedorn G, et al. Scientific names of organisms: attribution, rights, and licensing. BMC Res Notes. 2014;7: 79. doi:10.1186/1756-0500-7-79
Hrynaszkiewicz I, Busch S, Cockerill MJ. Licensing the future: report on BioMed Central’s public consultation on open data in peer-reviewed journals. BMC Res Notes. 2013;6: 318. doi:10.1186/1756-0500-6-318