If your poke hits you should have plenty of hit advantage to beat their counter poke with some of your launching normals or strings that lead to combos. If they decide to block after getting hit, you will get some pressure which often leads to 50/50's. If they block your poke, you're typically at a disadvantage, so you are better off blocking. If he blocks your poke and you try to poke back right after he will win if he decides to the the same.
Pokes are used to check your opponent and sometimes they can interrupt pressure if the poke is fast enough. As Kotal Kahn I will often use 114 into airgrab and then procede to check my opponents with d1 to see if they respect the +frames. Sometimes people don't respect the airgrab and they will try to poke me out of my following strings (mostly because my frametrapping is shit online).
They probably have more use but that's basically how I use them, but I'm still a scrub so I don't know everything.