T-score expresses the certainty with which we can argue that there is an association between the words, i.e. their co-occurrence is not random. The value is affected by the frequency of the whole collocation, which is why very frequent word combinations tend to reach a high T-score despite not being significant collocations.
When comparing the T-score and MI score, in most cases T-score is more useful than MI score. However, both of these scores are affected by the corpus size. This makes them less useful when working with modern mutli-billion-word corpora. This is why Sketch Engine prefers the LogDice score in most situations, especially in word sketches.
The T-score can only be calculated in the Collocation tool in the Concordance.