In MTG, there are several ways to win that don't involve damaging your opponent. The most prominent is milling (running an opponent out of cards to draw), but there are also special cards like Felidar Sovereign, Laboratory Maniac, Battle of Wits, and Barren Glory that introduce unique victory conditions.
I understand why these decks can be fun: it's a novel experience to build and play a deck with an entirely different goal, not to mention "Johnny"-fun to figure out how to achieve some of those goals. What I'd like to know is something else entirely: when is prioritizing an alternate win condition actually strategically advantageous?
Specifically, it seems like, short of all-in-one-go combo, pursuing these goals involves actively sacrificing tempo and card advantage. Take mill cards like Glimpse the Unthinkable, for example: the card mills a significant chunk of an opponent's deck, but it doesn't actually influence the board state in any way; in the vast majority of cases, making your opponent put ten cards from her library into her graveyard has no affect on her board presence or ability to make subsequent plays (in some instances, it actually helps her, too).
What factors affect the viability of a deck built around an alternate win condition?
Is it ever feasible (like, you-could-take-this-deck-to-a-tournament feasible) to build around an alternate wincon in something that's not just a pure combo deck?
How can one offset or avoid the natural card and tempo disadvantage baked into most of these cards?
When is it practical to include an alternate wincon as "Plan B" (or C, or D, &c.) in a deck with a damage-based Plan A?