Can unlocked phones use any SIM card?

I'm curious, could you elaborate on the capability of unlocked phones to utilize any SIM card? Is it a universal feature that applies to all unlocked devices, or are there specific models or brands that might have limitations? Furthermore, are there any potential drawbacks or considerations one should be aware of when inserting a different SIM card into an unlocked phone? Lastly, are there any steps that need to be taken to ensure a seamless transition and activation of the new SIM card?