Does Praetorian Guard play a role on battlefield?

[Frank]

So, the duties of the Praetorian Guard may have been quite complex. Also with the ever increasing power of Praetorian Prefects in civil administration the Guard certainly played a role.

Thats another good point. In late empire the praetorian prefects became even a pure civil function. Latest in 2nd century it becomes usual, that one prefect was a military expert, while the other an expert in civil administration and jurisdication. So I expect a much higher percentage of librarii, exacti, exceptores and such in a praetorian cohort, than in a legionary cohort. These librarii were soldiers, no doubt, but their daily tasks were administrative. Propbably a lot of praetorians of all ranks were working for the equestrians in the central administration of the emperor. Latest after the use of slaves of the domus caesari started to decrease. In the offices of procuratores in the provinces we see a similar situation: a mix of slaves, fredmen and soldiers, lent form the local governor, working as lower and midrank clerks.