Request coalescing can be incredibly beneficial for cacheable content, but for uncacheable content you need to turn it off! Otherwise you'll cause your cache server to serialize requests to your backend for it. Let's imagine a piece of uncacheable content takes one second for your backend to generate. What happens if your users request it at a rate of twice a second? Those requests are going to start piling up, breaking page loads for your users while your backend servers sit idle.
If you are using Varnish, the hit-for-miss concept addresses this. However, it's easy to implement wrong when you start writing your own VCL. Be sure to read https://info.varnish-software.com/blog/hit-for-miss-and-why-... and related posts. My general answer to getting your VCL correct is writing tests, but this is a tricky behavior to validate.
I'm unsure how nginx's caching handles this, which would make me nervous using the proxy_cache_lock directive for locations with a mix of cacheable and uncacheable content.