This has been discussed many times in these forums. Extracted from https://www.gnu.org/licenses/license-recommendations.html :
"There are only a couple of kinds of projects that we think should not have any copyleft at all. The first is very small projects. We use 300 lines as our benchmark: when a software package's source code is shorter than that, the benefits provided by copyleft are usually too small to justify the inconvenience of making sure a copy of the license always accompanies the software.
The second is projects that implement free standards that are competing against proprietary standards, such as Ogg Vorbis (which competes against MP3 audio) and WebM (which competes against MPEG-4 video). For these projects, widespread use of the code is vital for advancing the cause of free software, and does more good than a copyleft on the project's code would do."
General info about licenses: https://www.gnu.org/licenses/license-list.html#SoftwareLicenses
