Isolation IC's question

I will use 2 ic's as examples a pc817 4 pin opto, and a cd4050 cmos hex buffer/line driver. the question is if the power and ground are from the same source, will the opto provide any more protection than the buffer/ driver? at the very least the grounds would need to be common even if the opto is powered by a different source.

Generally if you have a common ground than an opto does not provide any additional protection. Optos are usually used when ground isolation is needed. An example is to convey the feedback signal from the output of a switching power supply to its input controller when the input and output are isolated by a transformer.