[douglas]

I arm my police troops for two reasons:
1) Force enemy players who want to capture my planets to actually take losses in their troop forces.
2) Have a ready-made ground invasion force ready without much advance planning. Need to launch an unexpected offensive and you'd rather capture than glass? Just round up some police troops and put them on the job, they can be replaced while the fleet is already moving rather than forcing the fleet to wait for them to be built in the first place.