If you’re running it charge only, and
If it has a B0 balance wire (not all do), and
If you’ve double-checked with a multimeter 0.0Ω conductivity between B0 and B-, and
If the JST connecter is rated for your max charge current, and
If the balance wire AWG is rated for your max charge current, then
you can safely not connect the B- wire at all.
And don’t forget to fuse your charge port.
It’s really handy to only have the balance connector and one small charge negative wire connected to the BMS, but not always possible. Frequently, one of those requirements will not be met. Usually the 3A rating on the JST connector excludes all 4A charging setups.