If you’ve ever thought about adding smart lightbulbs to your house, but baulked at the cost of replacing all 50 lightbulbs in your house, maybe you should try out some smart light switches instead. While smart light switches aren’t cheap, they can be had for the cost of two, or no more than three smart lightbulbs. This can massively offset the cost of replacing your house’s lighting with smart lightbulbs, especially if you have large rooms with multiple lightbulbs controlled by one switch, or you have multi-lightbulb fixtures like chandeliers. Many switches even come with dimming functionality built in.
In the long term, depending on the types of bulbs you buy, you may find that even on a single bulb fixture, replacement cost of lightbulbs may result in it being cheaper to replace the switch instead of lightbulbs, the extended life of current day LED lightbulbs makes this an edge case though. You may also find that in certain situations your light fixture makes use of non-standard, or just uncommon lightbulb fittings. This means you may pay a premium, or may not be able to find a suitable lightbulb with a fitting that’s appropriate.
Now that we know smart light switches are so amazing, why would anyone buy a smart lightbulb? Smart lightbulbs are cheaper than a light switch. Many people have single bulbs connected to a light switch, so it works out cheaper to just replace the bulb. Individual bulbs usually offer you the ability to dim them, getting around any limitations of your current hard-wired setup. Individual smart lightbulbs also opens up your world to color-control, letting you set different colors and rotations for your lighting.
If you do happen to have multiple lightbulbs in one fixture and fear having to turn them all on individually, most systems let you group them to be able to control them all as one unit. Some people also like the security of knowing they can just turn off the hard-wired light switch on the wall when things go wrong, instead of hassling with ladders and chairs to unscrew a lightbulb currently connected to a live wire.
So there are various reasons for both purchases, you will have to look at your desired setup and purchase what works for you best.