The ability to group profiles in ways that are other than family groups creates a powerful way of examining your data.
For example, the category I asked for, Kentucky Pioneers and Settlers, will allow me to get a picture of the other families that may have migrated to Kentucky with my family. It will only work if other people with Kentucky settlers also use the category.
Having a quick way of finding who else may be in a group along with your ancestor can help break down 'brick walls'. It is an application of a research tool called the FAN principle - Friends (or Families), Associates and Neighbors. Knowing who your ancestor associated with, and where that association took place (for the geographic categories) helps you understand their lives.
Another example - you find a newspaper article with your ancestors name in a list of people attending a military reunion in a city far away from where your ancestor lived - is it him or someone with the same name? The article only mentioned names, not specific companies or regiments. If you have him categorized into all the military groups he was a member of, then check those categories. If the other people in one of those categories are also listed in the newspaper article, then you have a clue that it was him. Without the category tool, you might spend hours researching the other names in the list.
Another example - I have an ancestor who was a shoemaker and an immigrant. He did not learn his trade in the city he migrated to. When I find out what city he came from, I can check the list of shoemakers from that place and look for likely candidates he may have apprenticed with, people who may have been relatives.
This is also why the groups should be as narrow as possible, otherwise the group is too large to be usefull. Having my ancestors names in a group of people who 'migrated west' does not help me, having them in a group that migrated to Kentucky specifically does.
This is why categories are important, and why people use them. I can't think of any disadvantages at this time, other than getting distracted by your research.