Akismet, which routinely screens all incoming comments here for spam, has intercepted 27,700 such items since its installation five years ago. This is, of course, a Good Thing, but spam comments, even if they don’t appear on the site, still take up space in the database, and have to be weeded out now and then to keep things running with some semblance of speed. To assist with this matter, I have been taking note of repeat-offender IPs, and have banned them outright.
How much difference does this make? It probably adds a little bit of overhead to each call to the server. On the other hand, one single range of IPs 126.96.36.199 through 188.8.131.52 is responsible for 25,900 attempts on the premises. (The log shows over 195,000 visits from banned IPs.)
This process, too, can be optimized: instead of just appending the newest offenders to the list, I spent half an hour yesterday putting them in numerical order. And it’s a good thing, too, since some of them were in the list two or even three times.