Size really does make a difference.
Some people love to paint miniscule paintings and enjoy competitions to see who can paint the best tiny painting.
At the other extreme are the murals on the sides of buildings.
Generally, the bigger, the better.
When your images are bigger they command more interest and allow a freedom of expression that is not possible in a small painting.
Remember: Variation of size of objects or shapes in your paintings is very important. Same-ness will kill a painting very quickly.