Clash detection is often sold as the headline benefit of BIM, and it does prevent expensive surprises on site. But a clash report is only as useful as the judgement behind it, and a raw list of thousands of clashes helps nobody.
Hard clashes and the rest
Hard clashes are two elements occupying the same space: a duct through a beam. These are what software finds reliably.
Clearance clashes are elements too close for access, maintenance or code compliance. A valve technically clear of the ceiling but impossible to reach is a real problem the model reports as fine unless tolerances are set.
Workflow or sequencing clashes are elements that cannot be installed in the required order even though they fit in the finished state. Software will not find these. Experience will.
Why raw reports are useless
Run detection on an uncoordinated model set and you get thousands of results, most of them noise: insulation touching insulation, elements clashing with their own hangers, the same clash reported repeatedly along a pipe run. Hand that to a design team and nothing happens, because nobody knows where to start.
The work is in the filtering: grouping related clashes into single issues, discarding false positives, sorting by consequence, and assigning each to whoever can resolve it. A report of forty real issues with owners attached is worth more than four thousand raw hits.
What has to be true for it to work
Models must be at a suitable LOD. Coordinating approximate models produces approximate results. Meaningful coordination generally needs elements modelled accurately with their supports and connections, which is where LOD 350 matters.
Everyone must model what they will build. A structural model missing connections or an MEP model without hangers will pass coordination and clash on site.
Tolerances need agreeing. What counts as a clash, and what clearance zones apply, should be set before the first run rather than argued about after.
Cadence beats intensity
Regular coordination during design catches problems while they are cheap to fix. A single heroic clash exercise before issue finds the same problems when changing them is expensive. Weekly or fortnightly cycles with a short review meeting work better than monthly marathons.
What it will not do
Clash detection does not check that the design works, that maintenance access is sensible, that the sequence is buildable, or that the model reflects intent. It answers one narrow question: do these things occupy the same space. Treat it as one tool in coordination rather than coordination itself, and it earns its cost several times over.