If you mean enable all 4 of NS's categories at once, I would be concerned that lightweight machines would grind to a halt processing all those rules even on a relatively light network.
The issue, as I recall, that I'm having with troubleshooting is that while I was able to find the rules, I don't remember where they're at now, the process of restarting snort to apply the rule changes, wipes out my manual rule changes with the NS application of its categories.
For me, I am and have been using other tools for ids and ips, that's not what brought me to NS, so I'm not really concerned about NS ips I only started looking into it because of a forum post and hit a brick wall, I think it's important for a well rounded distro but I'd rather focus on what's needed to get 7 out the door, like samba.