The phrase indicates a very high level of effort, going beyond the average workload. During tax season, accountants often work their guts out to meet deadlines.
Pro Tip 2/3
Emotional Stress
Using this phrase can express emotional stress from extreme efforts. She slogged her guts out during the competition and felt utterly drained afterwards.
Pro Tip 3/3
Physical Exhaustion
Often used to describe physical exhaustion resulting from hard work. Construction workers sweat their guts out in the summer heat.