Hi Paul,
Juan has pretty much hit the nail on the head, but the simple summary is 'don't worry - be happy'
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PixInsight aims to empower, not to embitter. If you ever feel that you might be trying to operate PI outwith the extremely generous licensing agreement that Juan offers, drop him a line. He will either accommodate you, or explain why 'it can't be done'.
For an amateur 'home user' there are very few restrictions, other than the obvious 'don't rip me off' type. If you treat PI the way you would expect 'your' software to be treated, you will be pretty much OK.
HTH