They might express loud voice or messy condition.
Dakuten itself was invented to distinguish VOICED sound from unvoiced sound.
カ(ka: UNVOICED) → ガ(ga: VOICED)
タ(ta: UNVOICED) → ダ(da: VOICED)
We have 4x5=20 letters which can be voiced with DAKUTEN (as you know, maybe).
タチツテト (tachitsuteto)→ダヂヅデド(dadzidzudedo) ※ヂ and ヅ are uncommon in modern Japanese.
Other than these, we do not use Dakuten as formal script.
The word "Dakuten" itself means "Point(s) for muddying sounds".
So we often use informally Dakutens for arbitrary letters, in order to express somewhat loud, messy, extraordinary or terrible.