I guess it would depend on which multi your using and the roll you need it for? The quality of video at night is not all that good on P3's and 4's but if you have a aircraft with FLIR or other night vision camera you can really open up it's capabilities.
Daytime scouting pretty much anything with a camera and some range can be useful.
I go to the hobby store by my house and there is local law enforcement in there all the time they fly the inspire. The tech told me they legally can't use it for surveillance in most circumstances but auto accidents skid marks etc. a aerial view is really beneficial and much mo cost effective than a helicopter. He was saying they can get traffic moving faster and still be able to get the pictures they need.
Yes . . we are working with a local Surveillance and Security company here in Ontario, doing industrial site security, flying fence lines, doing roof and storage yard inspections etc . . the new Mavic Pro is perfect for these tasks and will fall under less stringent rules ( under 1kg class) here in Canada
"Yes" there are definitely applications for UAVs in order to enhance security capabilities, reduce response times, and gain situational awareness more rapidly. We have, and continue to work with some very large companies in the US who are just starting to look at this type of technology solution. However, it looks like it will still be a while until we see large scale adoption/integration.