I use both. Roadbike for training/leisure/competing with spd-sls. I had approaching double figures of clipless moments before I mastered them, I'm not proud to say. Mostly slow or no speed topples. Touring bike commuting / work use and when roadbike is awaiting parts for repair. Flats that came as standard. I've argued before that there isn't a great deal of difference. I've achieved some decent strava times on both bikes, despite tourer being about 5 kgs heavier, more if you count the panniers.
However I've been fed up of the weather and have been going to the gym and using a wattbike. For the first time ever I'm able to measure my output accurately. I started with my trainers that I use with my flats and used toeclips on the wattbike. I then found you can remove the plastic platform that comes with the bike and clip-in so started taking my road shoes. It has made 8-10 watts of difference for me, in favour of being clipped on. Not a great deal, but enough to convince me that being clipped in is worth it.