What does System property -Xmx....m do?

What does -Xmx...m memory option in the "Supported system properties" do and how is it configured?

What will trigger memory shortages?

I have one server set to -Xmx1024m (twice the basic memory).
What impact/benefit does it have for performance, index handling, audio (including handling large hi-res files) or is it mainly for video impact.
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What typical values could be used without wasting memory?
I cannot find any detailed guidance.

[atc98092]

It reserves a specific amount of memory for the Java virtual machine. For most users, there's no need to change anything. Mine is at the default 512M and never have any issues. I don't have a huge library, only about 4000 titles. It might be of a benefit with larger libraries, to perhaps make browsing and loading media information faster. But it has no impact on transcoding, as that doesn't run through Java. It's a separate application (ffmpeg) that Serviio calls if needed.