My thoughts as CDN engineer: It can be a tiny amount more efficient since an async disk IO implementation might dispatch the file read() call to a thread pool,

My thoughts as CDN engineer: It can be a tiny amount more efficient since an async disk IO implementation might dispatch the file read() call to a thread pool, wait for the result, and then send the data back to the client. Makes 2 extra context switches compared to sending data from memory. Now if the user is super confident that the data is hot and in page cache then a synchronous disk read will fix the problem. Or trying a read with RWF_NOWAIT and only falling back to a thread pool if necessary. On the other hand rendering a template on each request also requires CPU, which might be either more or less expensive than doing a syscall. All in all the efficiency differences are likely negligible unless you run a CDN which does thousands of requests per seconnd. In terms of throughput to the end user it will make zero measurable difference unless the box ran out of CPU.