Vector, and why it matters

Photoshop works with pixels. Illustrator works with shapes described mathematically, which means they can be scaled to any size with no loss whatsoever.

The practical consequence. A logo drawn in Illustrator prints on a business card and on a billboard from the same file. The same logo made in Photoshop at 500 pixels is a blurred mess on the billboard, and the client discovers this at the printer rather than at approval.

So the rule is simple. Anything that will be resized, printed large, or used for years belongs in Illustrator. Logos, icons, illustrations, packaging, signage, business cards, anything for print.

Photoshop remains right for photographs and photographic composites, which vectors cannot represent.

Files stay small, because a shape is an equation rather than millions of pixels.

Colours are editable forever. A logo with a colour defined as a global swatch can be recoloured across the whole document in one change, which is what makes brand work maintainable.

The adjustment. Illustrator feels less intuitive at first, because you are constructing shapes rather than painting. That passes within a few weeks, and the pen tool is the main obstacle for nearly everybody.

Set your document up correctly at the start: RGB for screen, CMYK for print, artboard at the final size, and units you will actually use. Changing colour mode later causes exactly the shift you were trying to avoid.