The best and most important area in the shop to install security cameras is at the point of sale as that is where the cash is located, so that is where most fraud takes place.
Integrating your video surveillance with the POS system makes a lot of sense. This example shows a skimmer being installed by some shop thieves. Your staff may not be involved in the fraud at the point of sale. This fraud took three (3) seconds. Nothing would show here on the computer if the cameras had never been installed on the tills, it would never have been found.
This is a bit exceptional; as most of the fraud involves actual transactions. Typically a brother of a staff member buys a $30 book, and it gets rung up as a $5 remainder book.
With a camera, you have a video record of each transaction, the customer and the operator. So you can provide evidence that can be used to confirm the point of sale software. This is always a problem if the matter requires verification. For this, you need video e.g. you often hear this remark in court "The computer said that I did it, but many could have done it.." or "I gave you a $50 and you gave me a $20, okay the computer said $20, but I gave you a $50."
The computer can and does give you alerts e.g. high dollar amount and other dubious transactions which can alert you to possible fraud. At the very least, it can enable you to identify common mistakes or misunderstandings that can be corrected with additional training.
Also just the fact it is there has been shown to reduce theft.
If your system is not integrated then the archived video needs to be searched by date and time, which is slower and a pain.
PS if you want to extend what the cameras can do e.g. facial recognition analytics to identify known individuals; counting analytics to ensure that occupancy limitations are not exceeded or demographic analysis we could do that too.