Life Orb numbers are usually pointless.
Let's go with someone with 321 HP who reduces their HP to 319. A non extreme example. Ignore all damage.
After one attack, the 321 HP users loses 32 HP, leaving 289 HP.
319 HP loses 31, leaving 290 HP.
So, it takes 2 attacks to matter.
If you think you'll be surviving something after x attacks that you otherwise wouldn't, X being the difference between your HP and your lowered HP with LO factored in, then go ahead and use the number. Otherwise they're largely pointless.
Whatever happened to the Wifi Trade Center? That was cool!