I would define splicing as a means of permanently joining two or more electrical wires to enable uninterrupted current flow, and the emphasis has to be on uninterrupted flow.
Twisting wire ends together, using tape or connection boxes is fine for short term fixings, but if you need a reliable, safe and practical connection that you can be certain will always work for you, in my opinion you cannot beat a soldering iron.
That’s why I prefer to solder my spliced joints as I personally feel it’s the most reliable method of joining wires. I don’t be using off-the-shelf plastic connectors for a permanent join. As a belt and braces kind of guy, I use my soldering iron, wire cutters, flux cored solder, a sharp blade and a few simple techniques to achieve a good, solid, reliable electrical splice.
I'm no expert, just a keen amateur, but hopefully this video guide will cover the basics nicely and enable you to safely splice with confidence.