On my vehicles, the only “side effect” is I have to reset the clock, as it defaults to 12:00 when the battery is reconnected. I find this only a minor inconvenience, outweighed by the knowledge that I will return to a vehicle with a working battery. I have done this with a 2017 Chevy Trailblazer and not had any bad effects. One thing to consider though, is the keyless entry. You might need to lock/unlock the vehicle with the key, as the remote lock will be non-functional.
As far as drain protection, I have found that even small drains such as the indicator light on a phone charger left plugged in, can drain the battery after a couple of days. Also, there may be unknown shorts in the system that cause drain. During daylight, it can be hard to tell if an overhead light is accidentally left on, so disconnecting the battery is a nice way to make sure nothing will discharge it while you’re hiking. The 30 seconds it takes to disconnect/connect the battery is worth it if you are in the wilderness away from jump starts, roadside assistance, or cell service.
As far as theft protection, though it might not be necessary in modern cars due to the RFID chips in the keys, many people, especially hikers use “hide-a-keys”. Loosing your keys while hiking would be a disaster, so I usually hide a key under my car. Sure a thief who finds the key might be smart enough to pop the hood and re-connect the battery, but it does provide one additional layer of security. Or, perhaps I get robbed while hiking/camping, and the thief steals my keys. Again, my hope would be that he is too dumb to figure out that I disconnected the battery.