Actually, I want to backup my system as I'm new to Linux, there is that I will break the system. So, setting up my system from ground again due to some silly mistake I made is tiresome. Also I have separate Storage drive for personal files.
BTRFS.
I'm afraid about the compatibility of BTRFS ( not like system drive need any compatibility ). Does it have a good community support as ext4?
I take advantage of the free disk space savings and don't worry about disk space much. I'll clear out my download directory and maybe some caches when my disk usage grows beyond 80% (as reported in GUI tools). Running duperemove across my drive every now and then also tends to help a lot without deleting anything.
If I do run out of space, there are a few interactive terminal tools that'll point out the biggest files so I can delete them and save some space in a pinch. I practice, I just don't really think about it much.