Not all goods and services that you offer to your guests are actually offered by you, the hotel. It might be breakfast which is served by a restaurant that belongs to someone else, or a taxi ride that the guest wants to "put on the room".
To the guest, this does not matter, and all items on the invoice will look the same to him. But to your accountant, it matters! Those services must not be recorded as revenue, but as 'transitory items'. Transitory charges also never have VAT. This is collected by the company offering the service, and they also need to provide the detailed receipts and invoices for your guests.
For apaleo users, adding a transitory charge works just like adding a charge. Whenever posting a charge on a folio, you need to think about whether it is the hotel selling, or a third party (like the taxi company, or the restaurant). When it is someone else, chose transitory charge.
You can even set them up as services, if you have third party service that you sell regularly.