Can hardcoding parallelism in Oracle hints lead to sub-optimal performance We have a large Oracle 11.2.0.4 database (data warehouse). Our developers hard code parallelism into their queries e.g. (PARALLEL(16)). Multiple queries can be running at once, all with large hard coded PARALLEL hints. Is this limiting Oracle's ability to optimize degree of parallelism based on available resources? 

(Trying to figure out if we should stop this practice and let Oracle optimize/maximize for us).
Yes, yes it can. If the number of running parallel threads exceeds the number of CPU cores on the host machine, each of these threads will compete for CPU resources. This can be extremely inefficient and harm performance.