Certainly shouldn't do any harm I dont think. Best way would be to mysql-dump it first so you have a backup. Then you can replace it if you need to.

i just did this, 24mb, crikey.

Ah the dreaded LUM_IpHistory.

AFAIK, this is used for the Who's Online, IP History, and Statistics extensions, all of which I've got installed.

I decided to whip up a monthly clean-up script that runs via crontab. Maybe it'll be useful for someone. You should replace the DB, TABLE, MYSQL_USER, MYSQL_PW and LOGFILE variables to something appropriate for your server. The INTERVAL is in days. This script also assumes it's accessing the database on localhost:
#! /usr/local/bin/bash

if [ $# -ne 0 ]
then
echo "No arguments accepted to this script right now"
exit 1
fi

DB='vanilla'
TABLE='LUM_IpHistory'
INTERVAL=30
LOGFILE=$HOME'/trim-vanilla.log'
MYSQL_USER='sql'
MYSQL_PW='pw'
echo "Deleting records older than $INTERVAL days of IP history from $DB"
echo "$0 run at: `date`" >> $LOGFILE
/usr/local/bin/mysql -u $MYSQL_USER -p$MYSQL_PW -e "use $DB; DELETE FROM $TABLE WHERE DateLogged < DATE_SUB(NOW(), INTERVAL $INTERVAL DAY); OPTIMIZE TABLE $TABLE;" >> $LOGFILE


The crontab entry looks like so, which runs the script weekly at 2:40am. Any additional output the script creates is also appended to the logfile:
4 2 * * 0 /path/to/trim-vanilla-ip-history >> $HOME/trim-vanilla.log
To run the script monthly:
4 2 1 * * /path/to/trim-vanilla-ip-history >> $HOME/trim-vanilla.log