It's important to clarify that I'm not arguing against wireless charging across the board. In fact, I think it works really well in common household items like electric toothbrushes where there are no usability compromises; you use it for 2 mins and then leave it where you got it from until the end of the day...just like a traditional toothbrush.
OK, enough about toothbrushes and let's get into why phone wireless charging is not so great!
Can't use your phone while charging
Wireless charging, at least for the time being, does not mean contactless charging. You have to keep your phone touching the pad for it to charge, so if you want to you use your phone, you have to pick it up and thus interrupt its charging. There are some wireless charging stands that allow you to see the screen while your phone charges, but that still limits the usability of your phone and you'd still have to be facing the charging stand which is not the case outside an office setting like at your living room or in bed.
Slow and inefficient power delivery
Wireless chargers are waaay slower than their wired counterparts. Modern smartphones can take between 15 to 18 watts of power while charging through a cable while wireless chargers vary between 5, 7.5, and 9 watts. That's half the speed! Is that not worth the half second it needs to plug your phone into the charger? Some very new wireless chargers promise up to 15 watts of power but they'll always be one step behind the speed of wired charging.
The problem does not end there, wireless charging is very inefficient and uses more electricity than charging through a cable. While wired chargers do lose some electricity as they convert AC power from your wall outlet to DC power for your phone to use it, wireless chargers require two extra conversions! Electricity needs to be converted from AC to DC, then the wireless charger converts the DC power to inductive power and sends it to your phone which then converts it back again to DC in order to use it.
As you can see, that's not very energy efficient. If you want to check this yourself, read the technical specs of a wireless charger. For example, the LG WCP-300 Qi charging pad takes a DC 5V 1.8A input and delivers a DC 5V 1A output. That's a 0.8A lost in the unit instead of heading straight to your phone.
Takes up desk space
Most wireless charging users place their units on the office desk and on the nightstand next to bed. While you might have a large desk at work, nightstands don't offer a lot of space so you either don't have room for a wireless charger next to your bed or it will take up most of it!
Your phone vibrates right?
If your phone is put on vibrate, it will eventually move itself out of the charging area, and on some cheap wireless chargers it might fall off of them altogether. That said, not all wireless chargers are created equal and some of them design their units to minimize that problem but your mileage may vary depending on the size, weight, and the charging area of the phone you're using.
In the end, I hope those facts have given you enough insight about phone wireless charging to decide whether it's suitable for your lifestyle or not and have helped you narrow down the options for your next smartphone purchase!