What a .vecz file is in Vectornation by Zaweba
New drawings in Vectornation by Zaweba save as .vecz, a gzip-compressed SVG; opened SVG files stay SVG, and double-clicking a .vecz opens the app.

Every app has to decide what its own files look like. Vectornation by Zaweba made an open choice. New drawings save as .vecz, which is an SVG file compressed with gzip. Your work is kept in a widely understood format, just packed to take less space.
Two other rules round this off. An SVG you open stays an SVG when you save it, rather than being quietly converted. And double-clicking a .vecz file in Windows opens Vectornation.
Why SVG underneath
SVG is the standard vector format of the web, readable by browsers and by most drawing programs. Building the app's own file on it means your drawings are not locked into a private format. If you ever need to get at the artwork without Vectornation, a .vecz can be decompressed into an SVG that other programs understand.
That matters for the long term. A drawing made today should still be openable years from now, and an open format underneath gives it the best chance.
Why compress it
SVG is text, and text compresses well. A detailed illustration with many points, gradients and effects can make a large SVG file. Gzip shrinks it a great deal without losing anything, so .vecz files are smaller to store, back up and send. When the file is opened, it is unpacked and nothing has been lost.
When a file stays SVG
If you open an existing .svg, edit it and save, it is saved back as SVG. That is the polite behaviour when the file belongs to a website, an icon set or another tool. Changing its type behind your back would break whatever relies on it.
When you want a plain SVG of a drawing that is currently a .vecz, save a copy or export as SVG. When you want an SVG you opened to become a .vecz working file, save it as one.
Opening from Windows
Because .vecz files open the app on a double-click, they behave like any document in Windows. Store them in project folders, find them with Windows search, open them from an email attachment saved to disk. The Start screen also lists recent drawings for quick return.
Which format to keep your work in
Keep working drawings as .vecz. They hold everything the app knows about the drawing in a compact file, and Vectornation's own features, from version history to recovery copies, are built around your drawings being saved regularly.
Export to other formats for delivery: PDF for print, SVG or PNG for the web, AI or EPS for people using other programs. Keep the .vecz as the master you return to when changes come in.
Avoiding confusion
Clear file names help, especially when the same drawing exists as .vecz, .svg and .pdf in one folder. Windows can hide extensions, so turning on file name extensions in File Explorer makes it obvious which is which.
When you send a working file to another Vectornation user, send the .vecz. When you send to someone using a different program, export to a format they can open, rather than expecting them to know about gzip.
And back up the .vecz files. They are your source. Exports can always be made again, but only if the master survives.