My $.02: There are numerous types of fenders, depending on your bike, and tire selection. If you are the type of rider who rides every day, regardless of the weather - a bike commuter, or bike tourist for example, then fenders are a very good idea. I'm talking about the kind that bolt to your bike's dedicated fender mounts. Of course, that means thinking ahead and buying a bike that was designed with fender brackets and space for both your tires and fenders. But, most folks who fit this category, probably already have full fenders and know a lot more about them than I do. Then there are the rest of us, who have bikes that were not exactly designed for full fenders. I'm in that class. Since I sometimes ride in the rain on muddy dirt and gravel roads, I've decided to shelve my macho bike racer image and go for inexpensive SKS clip on plastic fenders when the roads are wet and muddy:
https://smile.amazon.com/gp/product/B000X61N2A/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1 .
These fit my Swiss Cross CX bike, are inexpensive, easy to install and remove, and do a good job of , well .... covering my ass. Good investment of $16. I haven't found anything for the front wheel though. A lot of the plastic front fenders are incompatible with my fork and brakes. There are some that mount to the down tube, but they wont work too well if you are cornering. Also, I already get some protection from my down tube. Frankly, if I could find something that would fit my fork and brakes, that would be as easy to install as my SKS rear, I might go for it. In short, in NH mud season, fenders are a very good idea.