In every day life yeah, it can make it harder to follow. If you're reading a hand written letter in all caps, it's not as easy to follow as a letter written using proper casing.

The military uses all caps to remove as much irregularity as possible. Standing a post on duty, you cycle through a lot of people. It's not just one person there all the time. Some posts have like 12 different people every single day. So when you open a log book, and you're going line by line, it can become hard to follow all the different handwriting. Between left and right handed, how you hold the pen, the rush someone is in, handwriting can very widely. So by using all caps, and keeping letters blocky, you remove a lot of the irregularities. So it's easier to read information line by line.