You can have retention without a retention strap.
In almost very situation I prefer a button or strap type retention system. IWB where I already have clothes in the way neither of those options is great so I often go without. If you are open carrying for whatever reason retention is also a plus. I really like the holster that has what looks like a button strap, but it actually just flips down. People unfamiliar with it will try to unsnap it for plenty of time for you to react.