The data files that Beat Saber uses organizes the timing of blocks in terms of # of beats - if there's a block on the 5th kick in a house track, the data file would say that the block is on Beat 5. This is how other mappers treat it as well.
Beatmapper uses bars instead; that 5th kick is at the 2nd bar, so it's given the number 2.
The big reason for being different is that most music is synchronized around bars. It's common for many songs to have 16 or 32 bars of intro, 16-32 bars of breakdown, 16-32 bars of drop, etc. I used to DJ, and thinking in bars is a much more intuitive way to think about chunks of songs. Incidentally, DJ software uses bars as well, as does the editor in Stepmania (popular editor for another rhythm game, DDR).
In 4/4 time, you can just multiply the bars by 4 to get the beat, so you might be thinking that it doesn't actually matter. A 16-bar chunk is a 64-beat chunk, and so you can think in chunks of 64 instead of 16, and it's the same thing. The reason this doesn't work is time signatures; a 3/4 song will have 3 beats per bar, and suddenly that same 16-bar chunk is 48 beats.
This is one of those things where I recognize that there will be friction for folks coming from MM or other mappers, since it's different. The community thinks in beats, not bars, and it's weird that the editor uses a different system from the files it produces. I'm considering adding a toggle to allow the user to switch between bars and beats, but I'm hesitant to add any new feature that isn't obviously valuable for a lot of people.
So, please respond to this post with a ๐ if you feel like this feature would be helpful, or a ๐ if you don't think it's a big deal / not a priority. Thanks!