Sure we have. It's bad because it puts the point of re-entry to the battlefield right at the feet of the force that can hold their ground. In an even fight, not too big a deal. It's something to plan around. In a non-even fight, as most will likely be, it puts the point of re-entry to the battlefield right under the feet of the enemy that has the most numbers. That rewards the Zerg by making them more of a Zerg. Summoning worked in Shadowbane due to many limitations, but also because the point of re-entry was at the summoner.