To use a resource without autoinstall, you must have a definition for that resource installed in your CICS® system, created using CEDA, DFHCSDUP, or a macro table. This clearly uses up time (to define and install every resource) and storage, because every definition occupies storage whether the resource is being used or not.
With autoinstall, you do not need to define and install every resource that you intend to use. Instead, CICS dynamically creates and installs a definition for you when a resource is requested. CICS bases the new definition on a “model” definition provided by you.