Matching has three constraints at once. Who is free, who is qualified for that role and who can physically get there for six in the morning: filling a shift from a spreadsheet is how the wrong person is sent.
Documents expire silently. Right-to-work evidence, certificates and licences have dates, and placing somebody whose document lapsed is a compliance failure rather than an administrative slip.
Timesheets are where the money leaks. Hours approved by the client, matched to the rate and turned into both an invoice and a payment: done by hand, some of them are always missed.
A no-show needs a process. Knowing who else is free and near enough within ten minutes is what turns a failure into a minor delay, and it is exactly what the client is paying for.