Thanks for posting your questions here. Since eBay is now automatically including the Gallery feature with all listings at no charge, it is no longer necessary to select the "Gallery" option within the Marketing Tools section to make sure your listings have a Gallery image once submitted to eBay.
Although you do not need to check the "Gallery" option when creating your new Marketing Tools profile, leaving that option selected should not have any adverse impact on the listings you post using that profile either.
I will mention this to our Product Management team so they can consider updating how this option is presented on our site to help minimize confusion of this nature.
Also, deleting all your old profiles will not have any effect on the listings you have created in the past, so you can definitely delete all your old profiles any simply build new ones from scratch if you would like.
I hope this helps. If you need any further assistance with your account, please feel free to contact our Customer Support team by mousing over the “Help” tab and selecting the “File Support Case” option.