There is a short-term gain with tinning, but it creates a long term problem. The better solution is to use crimp-on ferrules.
We don’t sell ferrule kits, but here’s an example you can get from Amazon:
Why is tinning a problem?
Tinning holds all the wire strands together, so it’s easier to get the end securely into a terminal. But the solder creeps up the wire, leaving a point further up the wire where the solder ends and the strands are free. That point absorbs all the flex of the wire over time, it’s a brittle point that breaks easily. So eventually (sometimes surprisingly soon) your wire breaks right where the tinning ended. Solid wire breaks easily, stranded wire does not. Tinning turns a stranded wire into a solid wire, but just for a short section.
Why do ferrules help?
The benefit of many individual strands is maintained, they are just bundled together inside a sheath that easily inserts into a terminal with stray strands. A good ferrule also provides some additional stress relief with an outer plastic collar. This minimizes strand bending near where the bundle tightens. Overall, the result is a very long lasting and reliable connection that you can bend and flex as needed.
Ferrules are recommended in all cases, but they are especially valuable in mobile applications (like costumes) where the wires move around a lot. Every time you flex a wire that is tinned, you are probably breaking a strand. Soon, they are all broken. With ferrules, you would have to flex the wire thousands of times (or more) before any single strand was stressed so bad that it breaks.
Use ferrules! Avoid tinning. :)