Wiktionary
vb. (context idiomatic transitive English) To behave in a manner which favours or which is biassed toward.
Usage examples of "err on the side of".
Kindan answered, not knowing what rank the man held and guessing that it was best to err on the side of caution.
Like most Belters, he had always felt the ARM tended to err on the side of caution in their role as technological police.
Ought we not err on the side of compassion and set her ashore without further processing?
And since you do not know which will go into the story and which will be left out, err on the side of generosity.
I don't know what's happening, and until I do I just want to err on the side of caution.
How much better was a topic of lively wardroom debate, but given that Captain Honor Harringtons eighty-five-thousand-ton light cruiser had taken out a seven-point-five-million-ton Q-ship, prudence suggested that Haven err on the side of pessimism.
I wasn't sure, and thought it better to err on the side of caution.