I have a laptop an desktop that both have Win10 on them and I was going to add Ubuntu 14.04 LTS 64 bit on a side by side install. I've seen lots of issues with machines that already had Ubuntu installed alongside Win 7 or 8, that showed up when attempting to upgrade to Win10.
I have not seen anything about problems of adding Ubuntu with Grub to an existing Win10 machine. Any dangers in doing this?
There is always a slight risk when dealing with partitions on a disk, and there is always that risk that you could corrupt your drive.
However, it will most likely work fine. The 15.04 installer has an Install alongside Windows option built-in, which means you may not even need to mess around with partition tables:
If you don't want to risk anything, I would suggest booting the CD/DVD/USB and using Try Ubuntu and see if you're happy with it before installing.
So in summary: YES there are dangers, but if you don't do anything, you cannot do anything wrong either (nor anything right).
