I guess that depends on how large the percentage of rejected passwords is and how fast the algorithm is.
brain doesn't make the H/s speed of your GPUs faster, that only depends on the OpenCL devices and tuning options.
but in general if cracking is slower than the network (communication) and the task of rejecting the passwords/tasks, hashcat will finish sooner.
You can try it yourself with a dict where you have 50% completed already and send to brain. The next time that hashcat starts it won't use those password candidates and skip them and continue with the second half (after the first 50% already done). This should be faster if network is not an issue and if the hashing algorithm is slow enough as explained in https://hashcat.net/forum/thread-7903.html (especially the sections "The costs of hashcat brain" and "The brain and the bottlenecks" are interesting for this discussion)
brain doesn't make the H/s speed of your GPUs faster, that only depends on the OpenCL devices and tuning options.
but in general if cracking is slower than the network (communication) and the task of rejecting the passwords/tasks, hashcat will finish sooner.
You can try it yourself with a dict where you have 50% completed already and send to brain. The next time that hashcat starts it won't use those password candidates and skip them and continue with the second half (after the first 50% already done). This should be faster if network is not an issue and if the hashing algorithm is slow enough as explained in https://hashcat.net/forum/thread-7903.html (especially the sections "The costs of hashcat brain" and "The brain and the bottlenecks" are interesting for this discussion)