But limiting for efficiency is usually done in a way that I would call a cargo cult: First, the number of items per "page" is usually a number one would pick per displayed page, in the range of 10 to 20. This is inefficient for the general case, the amount of data transmitted is usually just the same size as the request plus response headers. So if the API isn't strictly for display purposes, pick a number of items per page that gives a useful balance between not transmitting too much useless data, but keeping query and response overhead low. Paginate in chunks of 100kB or more.
In terms of computation and backend load, pagination can be as expensive for a 1-page-query as for a full query. Usually this occurs when the query doesn't directly hit an index or similar data structure where a full sweep over all the data cannot be avoided. So think and benchmark before you paginate, and maybe add an index here and there.