What are the negatives of setting a high wait_timeout setting in MySQL?
Idle and persistent connections will obviously take longer to expire. This may mean that you bump up against some default and sane limits.
The first one will be
max_connections. Then following that - because of the way which MySQL assigns memory and file descriptors to connections and threads -
open-files-limit and general RAM consumption will increase.
wait_timeout can act as a bit of a natural guard against these things. You can increase it, but bear in mind that the client-side is at fault and that it may have server-side impact.