Tracking a price takes one address per market. Checking an ad takes one per market, in separate profiles. Tracking a search position takes one per market, fixed over time. Testing an API takes one per region the API treats differently.
When it grows
The number grows when the destination limits lookups per IP and your volume passes that limit. Measure the limit with one address before buying ten. Bulk collection is the case that gets there fastest.
Several accounts take one dedicated address per account, because shared lumps you together with other people on the same IP.