Is losing a tempo always bad?

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BlcScorpion

Or are there exceptions, if so which?

Dodger111

Yeah in some engames and mid-game positions you gotta "lose the move" to win material or mate. 

Although I guess that's not exactly like losing a tempo.

Shamandalie1234

In openings it's bad if you don't get compensation for it (f.i. a pawn, an attack)

In the middle game it doesn't matter much.

In the endgame it can be a matter of winning or losing.

SilentKnighte5

No.

Triangulation is an idea when you purposely lose a tempo in order to win.  Look at the Q v R Philidor endgame.

Generally you don't want to lose a tempo though.  You'd have to have a clear and specific reason to do so.