What it’s supposed to do
I’ve heard working pros say a lens hood doesn’t do anything. And for their style of shooting it may not. For me the lens hood does a couple things that I appreciate. First, it helps improve the performance of the lens. It might be surprising but a lens hood can improve contrast even on a cloudy day. A thin layer of clouds can be really bright and that brightness coming from all over can increase veiling lens flare. It may not be enough to ruin your pictures, but it can influence them. If you shoot outdoors during anytime of day I recommend using a lens hood. Even if you shoot in a studio a lens hood is a good idea. The fact is any bright light source that is outside of the frame but in front of you can cause a lens flare. The last thing you want is to go through the time and expense of a shoot only to find you have lens flares from the strobes.
A physical barrier for your lens
Aside from preventing lens flare another good reason to use a lens hood is simply to offer some protection for your lens. It can help protect the front element from simple things like fingerprints and it can offer some protection from accidental bumps and drops. Finger prints can actually cause their own lens flares, as can dust. In my opinion this makes using a lens hood is a better way to protect your lens than using a front filter. Front filters are often prone to and worsen lens flare so my suggestion is to avoid using them to protect your lenses. Just be dilligent about using the lens hood and lens cap.
By now hopefully you’re asking why on earth would anyone NOT use a lens hood? Well, the truth is, they’re not the most convenient items, particularly on longer telephoto lenses. My Tamron 70-200 G2 has a huge lens hood but there are some things you can do to make things easier.
Factors of convenience
The first thing you can do is reverse the hood when you’re not using your lens. Yep, on all my lenses the hood can be reversed, that is you can literally place it on the lens backwards. With it on backwards it won’t take up nearly as much space in your camera bag, and you’ll have it with you at all times. Of course the lens hood does nothing when it is mounted backwards so don’t forget to flip your hood around when you start shooting.
Another option is a collapsible lens hood. A few companies are offering collapsible lens hoods that can easily be collapsed for storage then extended when you start shooting. This makes it a little easier to work with the lens hood, although it might not protect it as much from bumps and drops.
I hope this info helps you get the most out of your lenses, good luck and happy shooting!