Estimate space for game installs.
Store pages quote the base download, not the installed footprint. Day-one patches typically add fifteen to twenty-five percent, and shader caches and save data add a few gigabytes more per title. The peak figure matters separately: installers usually need scratch space to unpack into, so free space must exceed the final total by a substantial margin during installation.
Real per-game size
Size per game = base size x (1 + patch overhead) + shader cache and saves
Peak requirement
Peak during install = total installed size + 60 percent of one game for unpacking scratch space
The download is compressed, and the installer expands it. Patches applied on first launch add more, and some titles keep both the packed and unpacked data until installation completes.
Yes, but it will be rebuilt on the next launch, usually with a period of stutter while it recompiles. It is a poor target for reclaiming space.