I think it would be more convenient to have a preset number of units rather than having the currently selected group split into fractions.
We already have a hotkey dedicated to ordering a single unit within the selected group, but it would be useful to choose the number of units we want to command from that same group, so we wouldnt have to isssue instructions to them one by one.
Within the hotkey settings, an option could be added to select the number of units to command at once. For example, if I have a group of women selected, lets say 27 and I want to build 3 farms, pressing a certain hotkey would send 5 of them to build one farm. pressing it again would send another 5, and repeating it once more would send the last 5. This way, id only need to give 3 orders instead of 15.
If this feature is implemented, i suggest allowing us to choose up to five preset unit amounts to command at once. In my case, they would most likely be: 1, 5, 10, 20, 30.