It depends on the hospital. Where I work now, techs very rarely work in the ICU. If they are needed, it's because the floor has a lot of patients on insulin gtts and blood sugar checks need to be done Q30min to Q1H. They also help with baths. At another hospital, I worked as a tech. My home unit was med-surg, but I frequently floated to MICU/SICU and ICU step-down units. Most patients had central lines but I would start IVs or draw blood if needed. In the mornings I would go around and prep all of the tube feeding bags (for patients who were on them) because they were always changed at that time. For the patients who needed blood sugars, I did those. I did dressing changes, wound care, trach care/suctioning among other things. Nurses often did their own vitals or I&O's because they preferred to do them, which is fine. If I noticed any abnormals or if I noticed a drain or foley was getting full, I would empty it and tell the primary RN. Otherwise I just helped out where needed, or I would do a 1:1. I once sat with a patient with an IABP in place, so that was pretty neat, especially when the primary RN took the time to explain some of the settings and wave forms to me. I did learn a lot floating to the ICUs because the nurses would teach. The ICU step-down/PCU was similar to my experience as a tech working in ICU.
Where I work now, the techs on PCU do vitals, check blood sugars, help patients with basic needs/care/toileting, help answer call lights, help bring patients down for tests, help with I&O's. Techs on both units help with stocking supplies. I think no matter where you go you will learn a lot.