That kind of multitasking was one of the most impressive things about it. I could play four MPEG videos at once smoothly (with the interface and other windows still responsive) while Windows struggled to play one on the same hardware. That and it booted in 30 seconds including detecting and loading built-in drivers for all my hardware (Windows took 1-2 minutes and needed drivers manually installed).
I never used BeOS much though, as there wasn't much software available for it. This was in ~2000.
Even better, they had a real I/O scheduler. I could transfer video from a DV tape reader with a tiny buffer while Mozilla compiled in the background and while the compiler got slower the tape drive never stalled and the UI never lagged. That was quite a change compared to Windows or classic macOS where you had to treat the system as a single-app device.
It's easy to boot quickly when you have very little supported hardware to look for. I remember compiling custom FreeBSD kernels with only the hardware on my box and racing my roommate's BeBox to login prompt. Then he would start playing a bunch of movies at once and I'd open up Netscape.
