A quota half filled stops everything. Fieldwork closes only when the last hard-to-reach group is recruited, so watching which cells are lagging on day three, rather than day ten, is what keeps a project on its dates.
Incentives are a payments operation. Hundreds of small amounts owed to individuals need recording, paying and reconciling, and an agency treating that casually spends its own money and finds out at the year end.
Personal data outlives the study. Recordings, transcripts and contact details carry retention obligations and deletion promises made in the consent form, and honouring those requires knowing where everything is.
The margin is decided in fieldwork. Recruitment and incentives usually cost more than the analysis, so a project quoted on days of thinking rather than on cost of access loses money on precisely the difficult samples.