I ride with clipless pedals both on and off road. The advantage of being clipped in off road, especially on nadgery climbs is brilliant- being able to put in a toe tap or quick pull up where there isn't room to push down for example . What's more, on any off road ride you'll clip in and out more times than you can count. On a tight steep switchback descent a dab may be required and with the right shoes and pedals I can unclip, dab, and be back on the power in the blink of an eye. This translates into massive confidence levels, especially when you are used to being connected to the bike on rutted, bumpy surfaces. It teaches you balance and gives you a benefit of being able to use bodyweight to steer and alter line, pull up, hop and shift weight around the centre of gravity. I can do most of that on pinned pedals and specialist grippy shoes, but there are occasions where you lose a pedal, and the penalty is ripped shins!
On road that familiarity with clipless pedals means unclipping and clipping back in becomes second nature.