The downside of using soldering braid is that is untinned, and so over time the copper will oxidise and its resistance will start to increase. It won’t happen overnight, and you’ll probably get a minimum of several years use before there’s any effect on the signal. Where it’s only being used just as a shield (braid connected to ground at one end only) it will continue to work well at this, but where used as a signal conductor, you may notice hum levels start to increase over time. Then again it will be so slowly that you’d probably not realise it was happening.

Rate of oxidisation will depend on local humidity and pollutant gas levels, so it will happen quicker in humid cities than in dry country settings.

You can mitigate all this by tinning the exposed ends of the braid yourself with solder (once fitted) and covering the copper braid with heatshrink, just leaving the ends exposed for soldering.

So, it’s always best to be prepared and have at least one guitar’s worth of braided cable in stock if you plan to carry on guitar building or fettling existing guitars.