I am a big fan of storing all sorts of personal data, including my family tree, both online and also offline (in my computer’s hard drive). I like online access because of the increased security (assuming it is encrypted), the automatic backups, and the ease of access to the information when traveling, even when traveling to a local genealogy society meeting.
Simon Orde, the owner of the colorfully named company Calico Pie, has a different viewpoint. After all, he and his company produce Family Historian, one of the very popular genealogy programs for Windows. Simon has written an article that provides his opinions of online versus offline storage. I will say that his article makes a lot of sense.
If you have an interest in the topic, I suggest you read The Argument for Building an Offline Version of Your Family Tree by Simon Orde that has been published in the Findmypast web site at: https://goo.gl/SzM1Qi.