I think both printed and on-line guides have their uses.
On-line ID information sources can be updated as new information comes in (though too often they are not). They can handle huge amounts of information. They’re the only way to construct large multi-entry ID keys. Assuming there is no paywall, the information can get to lots of people world wide. (I love BHL – Biodiversity Heritage Library!) Access to on-line resources requires little space. So on-line is great!
On the down side, on-line resources can be ephemeral. If whoever hosts the information looses interest or funding, the whole thing can be lost. Changes in software can make the information unavailable even if it’s still hosted somewhere. The problem can be as simple as the next person in the job not recognizing that this hard disk holds something valuable and throwing it out or overwriting it. On-line resources are vulnerable to solar flares, power surges, strong magnets, and other problems that books don’t even notice. (Remember when iNaturalist went down due to a loss of indexing?) In general, there’s just one source for an on-line program, so if that’s lost, it’s lost. (Yes, there can be, probably are, back-ups! That’s how iNaturalist was able to come back on line after only a couple days. But somebody has to know where to find the back-up. Back when I knew about such things, the computer support for our science departments proudly backed everything up – on computer equipment sitting on the shelf above the main computer equipment. Anybody see a potential problem with that?) A number of on-line keys and other on-line resources I used to link to are simply gone.
Paper guides have value. They don’t require electricity, good internet connection, or even cell phone connections, so they can be used in more places. I think they’re more conducive to random browsing than on-line resources, much as paper maps give you information about all the surrounding area whereas the mapping programs on our cell phones do a good job of guiding us from here to there. Very importantly, books are more stable. They’re physically stable (at least if printed on archival bond paper). True, they can be destroyed by fire or bombs or insects, but they exist in lots of copies in multiple places, so one incident can’t destroy them all. If we do face the great apocalypse, descendants of survivors (if any) will be able to figure out information from books, but not from digital resources. I hope that won’t be relevant.
Of course books take up space and are heavy. (I remember a friend who was helping me move commented, after carrying boxes and boxes to the truck, “I wouldn’t mind if you read less!”) I’ve had to get rid of good books because I want to get others. I no longer get physical copies of botany journals, except for one. I’ve even published in an on-line only journal that can publish quickly, though I don’t like knowing that my (of course very important) work is just sitting on a computer somewhere. And then there’s one very useful book on fescue taxonomy for which relatively few copies were published. I’d really like to have a copy, but it’s simply not available. The best I’ve been able to do was order it from interlibrary loan (which many libraries no longer do!) and photocopy large parts of it.
And then there’s books as interior decorating. I love looking at my bookcases full of field guides and floras, some new and others very old, and thinking about the organisms I’ve learned about and the more that I could theoretically learn about in the future. :-)