Hi!
It depends. If you have only a plain simple search bar, without any filters, exclusions etc.. then it does not matter at all, you can add as many as you want, it shouldn’t have any noticable effect.
Still it is the best to add only those that are important to for search, to avoid unneccessary extra data.
On the other hand, if you are using taxonomy term filters, exclusions etc.., that unfortunately is going to be a lot slower as those queries can’t be indexed (only partially). While filtered queries are very well optimized and are executed in a single request, the database table joins and subqueries can’t be avoided, and those can’t be indexed either. Having more and more records and filtering them is going to affect the performance for sure. There are ways to mitigate that:
– Reducing the number of filters to a minimum
– Using drop-down or radio button based filters – less filter values = less subquery result set = more speed
– Avoiding custom field filters using LIKE queries – those can be painfully slow. Instead using “EXACTLY LIKE” as the operator may have a significant effect on the speed.