Writers and editors vary in their use of punctuation. Some prefer heavy or formal punctuation, lots of commas and a few semicolons and colons. Others tend to be more restrained, using punctuation marks more by rule than sound. You have flexibility, but it is best to show come consistency.
Example: The leader of the project was reluctant to change the schedule, but he did so at the insistence of his superiors.
But. Do not use a comma when the second clause does not have a subject.
Example, He fell from the balcony and hurt himself badly.
Example: If the expedition had come upon the signs earlier, it would have stopped for the night.
Example: The team worked on running, blocking(,) and tackling.
Example: I came, I saw, I conquered.
Often when the clauses are long, a semicolon is expected.
Example: They arrived at Mandalay, his childhood home.
Example: The old chief sat impassively, thoughtfully, giving no indication he was about to rise.