Why send a senior officer to scout?

Why would a Roman commander risk his second-in-command on a scouting mission?

Premodern reconnaissance depended on personal judgment, so a commander who could not go himself needed a trusted and experienced deputy to assess the enemy accurately.

Without modern communications or specialist intelligence staffs, senior commanders often conducted or supervised reconnaissance themselves. Personal inspection remained common through the Napoleonic era and still appeared in the American Civil War and First World War. A commander responsible for coordinating a very large main body could not always leave it to scout personally. Sending the most experienced subordinate available provided judgment rather than merely a count of enemy troops. The risk to a senior officer was real, but so was the risk of acting on a junior observer's incomplete assessment.