I'm good at grabbing people but let me tell you a good player during the laning phase of the game can avoid being grabbed. I've had several games where I just couldn't grab anyone during the laning phase. But Blitz is like the opposite of an initiator, during 5v5 stalemates you can often grab someone. Or if the enemy team starts rushing toward a tower and you and a few others are defending that tower you can grab someone immediately and eff them up.
Blitz is also the ANTI-escape mechanism. Nobody can run away I mean unless my grab is on cooldown nobody runs from me, ever. Blitz is also a great carry disabler, say a Twitch pops and starts attacking your team, grab him, fist him, ult him, GG Twitch.
Same thing if Fiddle teleports in with his ult, Grab, fist, ult. generally your team will also focus fire on who you grab even if it's a solo queue team with bad coordination they still target who you grab