Only exception was at a major roundabout where I struggled to get my foot back in after I set off, causing wobbling chaos as I went around!
I guess it depends on the pedal design - mine are one sided (Mavic Sprint, should you be interested) and when unclipped the weight of the back of pedal means it tips downwards and is then occasionally awkward to clip in on setting off
Sometimes it seems worse when I concentrate on trying to get clipped in vs. using the force and not thinking about it ...
Have you tried pedalling with only one foot clipped in until you are up to speed? (Lowish gear helps too

)
I came across this "technique" watching a pre race interview on TV - in the back of the shot was a cyclist just pedalling with one foot (pootling in the parc ferme or what ever the cycling equivalent is)
What i would like to achieve is a U-Turn - seen some pros do it almost within the length of a bike and at low speed