This depends on what kind of threats you're worried about and how far down the rabbit hole you want to go. AIUI the main concerns in this area are:
- If your security cams connect via wifi, they can be disabled by a burglar who has a wifi jammer. Some say that's becoming a common tool for miscreants to carry.
- OTOH, if your cams connect over wires, then anybody who can shimmy up to an outside camera and unplug it can plug in their own device and have access to your LAN.
- On the third hand, if somebody has broken into your LAN some other way, they could gain access to your camera footage, or maybe attack the cams directly.
The point of putting cams on a separate VLAN is that it offers some protection against both of the latter threats: jacking into a camera feed doesn't give access to your whole LAN, nor can someone easily get access to the cameras from some other part of the LAN.
My take is that the average homeowner probably is wasting their time/money to worry about any of these scenarios. But if you've spent money on security cams in the first place, maybe you feel like worrying.