Probes are the unit that always gets the first Chronoboost of the game and recently I heard of a post on Team Liquid about the efficiency of workers and minerals. However I could not find this post by searching the usual avenues. So I decided to do a few quick tests of my own..
Blizzard tells us three per patch, and after doing some research, this isn't the case. In fact, the number is lower. So Chronoboosting probes is beneficial early on, or during Maynarding(the process of taking half your probes and transferring them to your expansion). But there comes a point where Chronoboosting your probes helps you in no way relating to mineral collection. Here are the numbers:
My tests consisted of 1 minute intervals with 5 probes at a time.
5 Probes can collect 280 give or take 5.
10 Probes can collect 560 give or take 5.
15 Probes can collect 825 give or take 10.
20 Probes can collect 1040 give or take 20.
25 Probes can collect 1100 give or take 40.
So we can see, the most beneficial number of Probes to have mining is about 20. Any more and the number becomes erratic sometimes going up 100 a minute, sometimes only increasing by about 20-40 a minute. This is because all the Probes are trying to find empty mineral patches. I have even read that some Probes at this amount will bounce from patch to patch for up to 30 seconds without ever working. Therefore, Chronoboost no longer becomes useful on Probes after 20 Probes have been assigned to minerals. However this would change if you were doing a Fast Expand build.
20 Probes per expansion on the mineral line. Do not Chronoboost Probes after 20, which I believe is around the time the Core is going up if you had been constantly building Probes.An easy way to find out how many you have is to box your Probes and if there are two and a half lines of Probes exactly in the unit bar, thats exactly how many is most efficient.
|This is what 20 Probes look like.|
This also helps later on so when you see you have 60 Probes and only two expansions, you need to expand simply to be making more money.
I have heard several people say that you need to be constantly building Probes and never stop. But one Probe costs not only 50 minerals, but also 1 food. I have seen some pro games were the Probes made was around 90, thats half of your supply and at least 12 Stalkers worth of units. Meaning your army size will not be as strong compared to someone who only made 60 workers. Yes having extra can help you later on if you decide to go for 4 bases, or they do a drop in your mineral line, but thats what Cannons and keeping a good eye out for enemy movement is for. Chronoboost usually lasts for 2 rounds of Probe production on a single building So you may only need to use Chronoboost 7-10 times on your Nexus before needing to switch Chronoboost targets.
I hope this was helpful. For Terrans and Zerg, the Same rule applies to efficiency, however for Terrans, Mules take priority on mineral Patches over an SCV, meaning they will always work the same patch so make sure to assign them one of the patches that are closer to your Command Center.