Escape pods are generally used only in the event that a ship was damaged and facing imminent destruction. Starfleet vessels were equipped with enough escape pods to allow the entire crew complement to escape the vessel.
While all escape pods had the same abilities and purpose, different types of pods were equipped with different functions depending on their deployment. For example, the escape pods installed aboard the USS Exeter in 2376 were designed to have a emergency manual override on the inside of the pods, while the USS Excalibur, another Ambassador-class vessel, had the same functions installed on the interior of the starship. (NF novel: Requiem)
While all Starfleet vessels were equipped with escape pods, it was noted that several classes of Klingon design weren't equipped with escape pods. (ENT episodes: "Sleeping Dogs" & "Bounty"; DS9 episode: "Penumbra")