I have deleted images in digital cameras since 2000, and never had a problem. I asked a Canon rep, and a very knowledgeable lab rep about it. They both said there was no problem; however, both of them did warn of formatting or deleting images on a CF card in the computer. They advised formatting should be done in the camera.
The only problem I ever heard of was if you had a full card, to not start deleting images one by one.
I never rely on the camera LCD for an accurate evaluation of the image. There have been times I was shooting outdoors and forgot to change the ISO and/or f stop when I come back inside to shoot, So it is great to see that mistake immediately.
With all that said, the only time I delete is when a strobe misfires, or on those occasions I press the button before my brain is engaged, but usually I do not.
I am assuming those who do not delete images in your camera, you do it in the computer. That is what I have been advised not to do.
Here is what a Canon rep advised at a program I attended (I have no idea about what other manufacturers recommend).
New Card - format in camera before using.
After taking images erase individually, if card is not full.
Erase all images in camera anytime.
Never format the card in a computer
Never erase card in the computer.
Format in camera about every week or so.
This is not advice to anyone to delete or not.
.edit.... Clarification... I download the images on the CF card to the computer, eject the card, place the card back in the camera and erase all images while the card is in the camera.