Even if you use it to win lane your opponent still has global map pressure. He can stall you top while his team pushes an objective and tp to secure it as a 5v4.
Ignite seems like a very short sighted summoner for top lane. You win lane but then what? And if you lose lane with Ignite you are completely boned.
if you don't have ignite I can kill you get a lead make you lose cs run into your jungle kill your jungler and while you are trying to 2v1 me my team will take drag 4v3 yes I have done this more than once. trust me its reliable
to make the other top laner feel bad with monkey tower dives
what about 
If you want to go Flash/Ignite, it basically just allows you to get a lead large enough to where your opponent cannot do as much as you, even if they have more global pressure. If you are imposing on the enemy team, they will try to avoid you, try to kill you, try to get objectives far away from you, anything to get you away. This limits their options around the map. You can also use it on Shen and TK (because they have TP ults), but they aren't known for early pressure, so it isn't a great idea to do.
High lane pressure
If the enemy top laner is already behind due to losing lane and then TPs for drag you know what's going to happen? They might get dragon, but when he comes top I'll 2v1 him and his jungler if they try to gank me
