This makes sense but if you are using Gulp for legit reasons with certain projects there is something to be said for doing it for all your projects just to keep things consistent.
I don't know if I'd still do it for consitency. If I'm using mostly the same CLI tools, there's no much to learn and less code to mantain.
I'd stil not use Gulp if it's not really neded, which in most cases isn't to be honest!
You'd just do it for consistency when calling gulp watch or gulp build?
For some of my projects the build process is pretty complex and gulp provides true value. However, after thinking about it more you could alway standardize on build through package.json script and if gulp was needed you have package.json refer to the gulp build.
That's true, and just call gulp from package.json :)