In my opinion, it is, because it can show investors that the team is ready to bring huge results and has future plans.
As an example - KickCity, event platform where each user is rewarded for event promotion. You can try it today. More information you can find here https://medium.com/@kickcity_io/kickcity-public-beta-5aa66fafc5c7
Yeah it's actually very important. But you Can See some startups might not have the funds to run some certain aspects of the project that's why an IEO or ico is required. It's very good if a startup as committed some of efforts in having a working products before hosting an IICO/IEO, by this way investors will have faith in them due to their seriousness.