SUMMARY:
Doesn't have the 3 second delay.
It turns on only the result bits, it doesn't combine them with the bits that are currently on.
It's for bits that override each other when other bits are on.

Example games that use them:
1.  Dark Cloud 1 and 2.  You can't have more than 1 status active at a time.  You can't be poisoned and paralysed, or be boosted and be covered in sticky goo.  Only 1 status ailment can be on.

An example, even though it isn't necessary:
0042dac4 00000014 (your result)
0042dac4 000000ef (what is currently on)
0042dac4 00000014 (your result after you activate this function)

							    a
200ffc50 8f0d0004 lw t5, $0004(t8)            Loads the address you are testing.
200ffc54 930a0008 lbu t2, $0008(t8)           Loads the result bits.
200ffc58 03e00008 jr ra
200ffc5c a1aa0000 sb t2, $0000(t5)            Replaces whatever was on with only these bits.