I'm not sure if I'm the only one who doesn't know, but seriously, I can use my tennis shoes in biking?
The shortfall with tennis shoes is the very flexible sole. You waste energy by constantly bending the shoe on every pedal stroke. Is it an earth shattering difference? No, but in all-day use, it's probably significant.
Straps, grabby pedals, clips and straps and clipless can all be used effectively. The only time I'd highly recommend clipless is on a low racer recumbent, where you can break your leg if your foot slips off and catches on the pavement. I also think they're good on a standard recumbent, many find they reduce foot numbness. Otherwise, use whatever pedal/shoe system you prefer.
I also have found that MTB shoes (recessed cleats) are fine for walking moderate distances. That considers use on days off exploring the city, visiting museums, etc. At least I haven't had any complaints, with any of the three pairs of shoes I've had.