Is there something negative that can happen if I don’t check the box?
Without crop, the image will be resized base on one side only, depending whether the width or height is bigger. This will result in not square image, IF the initial image is not.
..and loaded a new image ..and the size was perfect, no cropping.
When the settings changed, it only affect the newly upload. So from that I can only assume the initial image is square, or the image is not square but almost, or the image is not square but the CSS of the theme forces it to be square ( looks squeezed ).
That accomplished what I wanted this time, but how might this affect me in the future with other image uploads?
Each theme is different. To find out more, please open a new ticket for this and link to your site too. I’m sure someone will be able to provide more details specific to your site.
Post it under How to and Troubleshooting
https://www.ads-software.com/support/forum/how-to-and-troubleshooting
or post it under your theme’s sub forum.