Manual testing is one of the core processes done for all the applications before it goes live.
Web, Api, database validations can be done manually for the existing ( not yet automated) and new apps( automation would be dome later once the app is stable with the new feature.
Web – Lets say if the applications are or E-commerce or Financial applications
the features for the anonymous users and registered users are to be differentiated correctly.
Ecommerce – order placement
Banking – Login and check the available balance, deposits, statements, loans, mortages etc basic necessary features.
Coverage and traceability to the requirements hold the key on what core features to be tested in lone with the time available