That symbolic Euro is important because it makes the deal a purchase instead of a gift. Legally, the consequences are significant.

There are numerous situations when paying nothing for something is entirely reasonable, for example when you are getting nothing (or even worse) in return (eg: bailout), or when you are giving something else in return (eg: future cooperation, access to new technology, access to a new market, etc.)

In my experience, the business side of startups is just making stuff up. That is to say it feels that way. The world of business kind of is a giant ambling collaborative novel.