Half-life over Cointegration?

In spread trading, I learned that two conditions are necessary:

1. Correlation between the legs.
2. Cointegration of the spread.

Internalized that as gospel. I recently learned that the half-life can also be considered.

Half-life is a measure of how long it takes for a spread to revert to its mean.

For example, if a trader is considering a trade where the legs are correlated, but the spread fails the cointegration test, he can still take the trade if the half-life meets his requirements. If the half-life is relatively short, then he would take the trade.

Furthermore, the half-life can be used to gauge whether to exit a position (e.g., stop-loss).