"Wireless" has more than one meaning.
Some companies talk use the word "wireless" to mean "not wired" devices, like door switches and motion sensors that do not require a wire that runs back to the main panel's circuit board. They use switches that transmit a radio signal back to the panel. Some companies use the word "wireless" to mean "no landline phone is required" because they use cellular, radio, or internet connections for monitoring. Some companies probably use it in both ways. Confusing? Definitely. It is probably not intentional. What is often intentional, though, is the presentation of wireless as being superior to "not wireless." But is it always superior?
In the case of Wireless Devices, there are pros and cons.
Holes in the wall.
Some companies say that installing "hardwired" systems puts hole in your walls and that phrase, when said in a certain way, terrifies homeowners and renters alike. Skilled installers fish wires through walls and only put holes the size of a quarter in the spots where devices will be mounted over them. No one will see the holes, and they could easily be filled with spackle/joint compound if you wanted to remove the system in the future. This happens, but only because homeowners are convinced to "upgrade" to wireless systems (because of the inference that wireless is inherently better). Wiring has actually been a great investment for homeowners, allowing them to upgrade system components without buying a whole new system.
Discontinued wireless parts.
It has happened before and will happen again. Major manufacturers discontinue product lines, and replacement parts become unavailable. If your system is comprised of all wireless devices, this could mean that you will have to replace your entire system if parts go bad.
Hardwired system components don't keep you from upgrading to new panels and keypads. Some companies may not offer systems that are hard-wired or hybrid (both hard-wired and wireless), but that doesn't mean they are better. It may mean that they don't have skilled installers capable of wiring.
That said, there are some companies offering devices that convert hardwired items to wireless in cost effective ways. This would be a route to try if you wanted specific features that were only available on a particular wireless platform.
Wireless components require battery changes. It may be only once a year, every two years, or maybe even every five years-- but battery changes are expensive if you have an all wireless system, and they may be needed at inopportune times-- like when you're trying to leave on vacation, or the middle of the night. If you don't mind changing them out on a regular schedule, before each one goes bad, wireless may be perfect for you! If you want to postpone expense and wait until the system makes you pay attention to it (beeping and flashing, and sending low battery signals you may get called about) wireless may end up being a hassle.
If you pay a company for labor to come out and change batteries, or for a trip charge, factor that in to the cost of a system if you are shopping for one or considering upgrades. Don't ignore trouble lights on your keypad-- they may be trying to tell you to change the batteries!
In the case of Wireless Communications, there mainly pros.
Con-- it usually costs more.
You get better security, but it costs more. Some companies only deal with cellular, some will do both, but all would agree that wireless communications are becoming the standard. We'll use a landline when a homeowner insists, otherwise, we include cellular.
Pro-- it is more secure
No lines outside the house that can be cut to disable communications. Not dependent on the security of the connections down the block that you see left open or run over frequently. It would take a more planned approach to manage to disable communication through a cellular communicator. Sure, outages occur periodically, but they do with landlines too-- you just may not be aware of them.
You don't need to pay for a landline
Over 1/3 of homes have abandoned landline phones. Telemarketers and survey companies have fewer and fewer landlines to call, so you actually do get more calls now than you used to. If you need a landline (traditional) phone for other reasons, keep using it. If you are only keeping it for your alarm system, you may want to rethink that. It is cheaper to add a cell communicator than to maintain a landline, and it is less trouble that VoIP lines that are not reliable for alarm communications. Most of our alarm service calls are for phone line problems or battery changes. Switching to cellular reduces service calls-- better for us, and better for you.
So, is wireless better?
The bottom line is this depends on the location and the particular building the system is in. Wireless devices may be the only way to connect doors and windows to a system in an all-finished house. A home with an existing hardwired system might face a bigger upgrade cost if they switch to all wireless than they would if they went to a hybrid system. A house with no landline or incompatible VoIP may need a cellular communicator. Another house may have to use a landline because cellular signals in the area are poor. You really can't say wireless is always better or worse for every building in either meaning of the word, but you can choose wisely for your home and situation.