Electrical cables need to have particular connections to be safe - they need to be clamped, and the insulation must remain intact and completely surrounding the electrical wires it protects. Often I see an electrical cable improperly stripped and connected.
This is most common under disposals, but behind the dryer, I think, it may be even more important.
Rubber insulation around electrical cables is very important.
Look at any electrical cord. It is insulated!
Most electrical cables have three individual wires inside - the hot black, the neutral white and a green ground wire.
They are bound together and protected by the insulation.
When they are put into an electrical junction box, fixture, or appliance, that insulation should still be intact!
The installer forgot an important step - the connector clamp.
Electrical appliances all come with a connector clamp in the box or kit.
See the round hole behind the dryer? That separable plate is supposed to receive a clamp, screwed in before the cable is installed, with the screws loose but still attached.
The cable would go through the plate and screwed clamp, until the insulation is securely surrounded, and those screws tightened. The electrical connections would be made and that plate would itself be screwed to the back of the dryer.
NEWER DRYERS HAVE FOUR WIRES, NOT JUST THREE!*
In those cases the clamp can accommodate the fatter cable.
This step takes an extra two minutes! Many installers don't care and discard the clamp. Many installers (homeowners and Uncle Bob) don't know and discard the clamp.
AND WHEN THAT HAPPENS, THE INSTALLATION LOOKS LIKE THE DRYER ABOVE!
Seeing the insulation properly surrounded and the clamp securely installed is certainly BEST PRACTICE.
The reason I say it may be more important behind the dryer is that it utilizes a cable carrying 220 volts and packs a good punch! If that dryer gets moved about, and the sharp edges of that opening cut into an exposed wire, it might make for an interesting drying experience!
My recommendation: check under your disposal and dryer and see if the cable was stripped leaving insulation in place and that a clamp was properly used. If not, you will know it was not a professional installation. The clamp not only holds the cable in place, but also fills the hole such that IF a spark is created it is contained in an area intended to handle it. Any spark getting out is about 2,500F and can ignite anything!
* Dryers are shipped now without plugs. This is because some houses have a three-hole receptacle and some have a four. Last summer our dryer fritzed. Going to the store, and knowing about the three vs. four cable dryer plugs, I bought a dryer and the gentleman asked when our house was built. I said 1998. He said, "You are just on the cusp of the change between the three or four-hole dryer plugs. Which do you have?" AND I DIDN'T KNOW! I had never looked! He said, "You probably have a four, but call me if you do not." When I got home I looked. It is a three-prong hole! So I called right away...
That is proof, yet again, that home inspectors don't look at their own homes, but instead other people's. Busted.