As an Agile practitioner and advocate, getting working software in the hands of users ASAP is a critical part of Agile's success in product development. However, once our external clients were involved are Sprint Reviews, it became very apparent that we (the product managers) should have visual insight and confirmation well before the client.
To accomplish this, we have our Engineers conduct mini-Sprint Reviews whenever a feature is completed and passes their Unit Testing.
Tactically, we schedule a Sprint Demo every day for 1/2 hour so the product internal stakeholders have their calendar booked but we determine whether we should actually have a Sprint Demo during the Daily Scrum meeting. We average 1-2 actual Sprint Demo's a week, usually 15 minutes long.
1. Internal Product Stakeholders are able to review and provide feedback on completed features - visually
2. Team Burn-down Confirmation - when an Engineer updates remaining hours to 0, the team knows the feature is completed
3. Quality Assurance gets better insight into what the feature is supposed to accomplish
1. Unless the team is disciplined, scope creep can occur as product managers visually see useful enhancements that were not identified during Sprint Planning
2. Extra team time spent (although benefits are well worth it)
Our experience has been increased productivity, as if Engineers were completely off the mark, we have a chance to re-work during the Sprint instead of during deployment.