Short answer
Exports include associations as columns: each associated object gets its own column. HubSpot's KB says the default is up to 1,000 associated record IDs per association column plus the associated record name; CSV exports can include all associated records. Choose between properties and associations in your view, all properties (no associations), or all properties and associations. Export permissions are required.
1. The export dialog
Exporting all companies in my demo portal: 4,624 rows in 1 file. I closed it without exporting.

2. Tips
- Clearing Include associated record name makes exports faster.
- XLS files cap columns at 256; use CSV or XLSX for wide exports.