When using the Parallel processing option in FME the number of threads always depends on the number of cores of the machine. For example 'Moderate' is one process per core on the machine. If your machine has a tonne of core you can potentially get a tonne of threads. This is really nice on one hand but on the other hand maybe you want to restrict the process to just a few threads. Especially if the process is memory intensive and the machine perhaps doesn't have enough to support so many parallel threads.
If you want to restrict your process to a certain number of threads then you need to do a few backflips in order to figure out which level or parallel processing to use and in the end the least you can use is half the number of available cores.
It would be pretty nice to be able to just specify the number of parallel processes you want to be able to use.
In addition, it also would be helpful to limit the number of threads so you don’t use all your licenses on one process. If I use any sort of parallelism in FME, the minimal parallelism still will use 16 threads, using up all my licenses.