I find lm-sensors to be mainly useful in combination with stress testing, since I want to evaluate cooling at full load. I'd prefer lm-sensors in the cpustress image, or alternatively cpuburn/prime95/... + lm-sensors in pmagic (the latter is probably easier, but harder to use since you have to start the stress test and figure out the number of cores yourself). Not much point in having one image with tools to stress the computer but no way to monitor it, and another image to monitor it without being able to stress it.
Since I don't usually have a climate-controlled room available, knowing how close a CPU is to the Tmax is the only way to know if it will survive a hot summer day.
I've previously used StressLinux
for this purpose, but by now it's horribly outdated and quite large for what it does. I've also hacked RIP (the CD version) to include this functionality in the past, but it was quite labor-intensive.