I've had a think about this after seeing the FGF thread. I've always used one because I'm really only a beginner, despite coming into my fourth season now. As I've moved up the grades in racing, I've encountered many circumstances that have required serious backpedaling to slow down quickly. Also we don't have a really good structured training at our track, so there's also a lot of circumstances there that have meant washing off speed quickly. I'm not a gear hound. I haven't changed my sprocket in over a year. I have found that changing the chainring has been fine for me, and I have handled the ~2GI jumps in gear ok. I also raced indoor on the boards over our winter that has just finished, and have been finding my legs so to speak in respect of gear choices with a bit of broader experimentation.
Now that I have moved up the ranks, after thinking about it, I could easily survive without a lockring in most racing. In the higher/better grades there is far less of the silliness that comes with the more inexperienced grades. The racing is much better. I will still use one for the reasons at training as described above, and because thus far in my racing life, an extra minute or 2 concerning myself with a lockring is of no hassle to me.