I am convinced of the conceptual and visual value of Gantt charts in Project Management.
These charts encourage us to structure the project and that in itself is a key benefit. The structure can hold several levels of details, display the dependencies between tasks, and show their estimated and real durations, highlights the critical path for the project. The Gantt can also allow us to define and visualize key milestones in the schedule, to see at a glance the overall tasks list and to see the progress made (if %completion and target dates updates are done effectively).
Personally, I tend to use Gantt Charts from the start of the project starting with a paper pad or whiteboard. The Gantt chart is a good tool to visually breakdown the project into deliverables and phases, to sequence tasks, to review completeness. I start it at a macro level and detail it as team members get involved in their specific parts of the project. On large programmes, it may be more effective to have different levels of Gantt Charts at the projects' level for the day to day project management and a more synthetic one at programme level for high level communications. In this situation, I found that the tricky part is to keep these two views in sync and it is not hardly possible to automate this.
During the project's life, detailed Gantts are useful to communicate more effectively with project teams on their tasks (contents, deliverables, estimates), to put in evidence the critical path and to follow progress made versus what remains to be done and to compare these to the initial baseline.
Just like any other tool, the Gantt chart has limitations and it can lead to some mistakes.
The most common one is to be driven or sidetracked by the softwares that you use to create it. Indeed, these Gantt tools are often very rich in functionality and they can consume a lot of the most precious resource of the project manager: his thinking time. Also, if they are not timely and frequently updated (at least weekly), they become outdated real fast!
PS: Another advice on this topic written by John Jeffreys can be found on pmHut.
I've been leading IT projects for more than 20 years at telecom and computer manufacturers: Thomson Sintra, Digital Equipment, NCR, Nortel Networks, Orange Business. My passion is Project Management and leadership and I run a blog on the PM best practices at http://dantotsupm.com/