Yep, Pretty much agree with Kent. Small waves and lighter winds - go unstrapped. Waves over head high or in strong wind/choppy situations, straps are nice.
If the wind is onshore straps are essential. In winter in big swell and onshore winds you won't be able to get out without straps to climb over the large foam walls or boost over closeouts.
Strapless allows you to be able to trim the board with foot placement more in light conditions and makes the deck 'clean' when you are learning to gybe.
Don't limit yourself to either, but rather explore and exploit the advantages of both by assessing the conditions and then choose what will ensure you have the most fun on the day.

Good winds,