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Can any explain in simple words what is the purpose of this latest
builds v1.5.0-dev-3388-g3b380148e ( NSIS: Fix uninstaller issue with shortcut removal )
and v1.5.0-dev-3389-g6e22efe79 ( NSIS: Don't pack files twice - reduces installer size to 7MB ) ?
Do I need this ?

No. The last several commits have been preparation for 1.6 release. Technical improvements have not been made for a while now.