I do in some tanks:
2. Injecting CO2 does not necessarily mean that all plants have access to all Carbon they can use. The carbon levels at different areas of the tank depend on your specific fish tolerance levels, how much and how you inject, what your flow patterns are, which plants are first in line, your water temperature and related O2 saturation, and who knows what other factors.
Does dosing Excel in addition to CO2 provide any tangible benefits? I do not know.
Conversely, statements that it does not, without supporting data, stll leave the answers debatable.