Its a game ender for sure when your already ahead, and lock both of the portals.

With cata's it can be tight but not finish the game.

But with Giants, if you manage to cap lock a portal vs the enemy its very hard for them to make a comback.

Depends on the map a lot too. In Cataract, it's very easy to make this a game ender, but on maps like Prison, it's very hard to keep those flags under control, since it's so easy to move between them.

You cannot have giants before catapults so I disapprove of your usage of "and/or" in the title.

I think it is the most powerful strategy.  That is why I don't really like playing maps that allow this backdooring like Cataract.   I'm sure there are people who will like it for different strategies, but I prefer maps like Exile where you can't capture the portal. 

The funny thing is that this is the strategy we used against the opponents in one map. However, it was our creeps (catas AND giants) from both of their portals attacking their citadel vs. 2 Rooks beating down on our citadel + however many of their catas made it through. The 2 Rooks won.

I'm almost certain we had the same Structure Health upgrades, though that could've made a difference.

It is extremely powerful and meant to be so. Cataract is the map where I see this the most. However, you can easily counter it by getting the portals back and locking them for one thing. The other thing you can do is do the same thing to them.

At some point, the game has to end. Without giants and catapults it would drag on too long.

The problem is when your team mates just don't understand the importance of this and ignore portal control. If you are one guy trying to secure 2 portals against 2 foes that are splitting their efforts and your team mate is off farming creeps like a dork or taking down some non critical structure at the moment, you will pull your hair out.

If I am securing one or more portals as Oak, I usually tell my team mate to go ninja theirs, to pull some heat off. However, a lot of people just dumb and think they can somehow overcome the creep waves even though at that point they can't.

So yeah, portal control late game is key, as it should be.

It's the most powerful and it's meant to be. You should NEVER let the ennemy take control of your base flags, NEVER.

We were ahead in levels and money but they got to the flags without us noticing due to the FOW making it hard to notice. 

We ended up doing it to the enemy too in order to win the game.  But I realized it was a mistake to let them do it to us first, twice. 

This happened to us on the map Mandala in a 2vs2 game. 

How are you supposed to keep your flags under control on such a large map with the FOW playing a factor and you don't have a lot of players to uncover most of the FOW naturally?

taking someones portals takes a huge drive or horrible map control on the team whose portal got stolen. So yeah it can be a game ender, cause its damn hard to pull off vs a good team.

Basic stratagy that I always inform my teammates of on Cataract is to destroy the towers leading up to the enemy portals as soon as they're capable to, and then just sit back and get the warscore up. As soon as giants are unlocked, go capping those portals. If the opponents try to lock the flags, then you just wait it out. If they keep locking them as soon as they unlock, they're probably concentrating all their forces on that one portal. Warp over to the other side, cap and lock that, and then move back to the original portal and take that one while they deal with the other one.

I wonder if I were a victim to you. When my team was ahead, I thought I would end the game by stealing the portals with my sedna general. I let my minions attack the creeps while I healed myself through their towers and stealing the portal. The problems was that I was pretty much a free kill without my minions, all by myself in their base. The beast was coming closer to me and I just couldn't run away.... it was horrible.