As soon as you place your work on the public web, you lose the innocence of not having to pay any heed to copyright. Your work may be used for any purpose unless you take care to control what others may do with it. There are no effective physical means to prevent anyone who can see your images from copying them, perhaps using them commercially or on sites and in ways that you personally disagree with or find abhorrent. Your copyright is the only tool you have to restrain such things.

Copyright is unfortunately deeply tedious and dull, and the temptation is to allow any use without considering the possible consequences. Some people have utilised the Creative Commons licenses to formalise their generous wish to share to an extent that they find acceptable whilst reserving rights they wish to retain. This is certainly worth considering, but be aware that Creative Commons licenses are complicated and consequently widely misunderstood even by some of the people who use them. They are also interpreted quite often as a sign of someone who is unlikely to enforce their rights, so may be safely disregarded. All told, it's simpler to use a copyright statement and require people to ask for permission.

Ultimately you have to decide whose photos they will be. They are yours by right, but unless you take care they will be taken from you by opportunists who have no interest in you, and whose only interest in your work is how much profit they can make. Any photograph that is good enough to use commercially or steal is not worthless.