Simple question, the ability to put poison into anothers pocket...Is this perk of any real use?

weaken people before a fight?
over then that i have nothing

Nah.It's cool. I always reverse pickpocket a paralysis poison and jump around that stupid bandit. In other case. If you want to roleplay a thief no-killing mode (good times) you could use it in some situations were guards are looking directly at a door. Pickpocket paralysis -> sneak through door -> poor sod never knew what hit him.