How to determine the "correct" scale for your art project?
Deciding on the scale is part of the design process
When you decide to make a piece of art its size is part of the design process.
There is a huge difference between a miniature and a way more than lifesize piece of art in the materials and tools needed and in the structure which may not be seen but is needed to build the item, but not in how you design the piece of art.

Often the size is decided by how much money the artist has to spend on the project or whether someone is sponsoring, has given a commission or guaranties the cost of the project.

Even huge artworks mostly have a smaller sample made, either as sketch or as miniature to show and get financing or as a way to work out technical difficulties. And most of those models can handle two or more out of those in one small version.

For the more modest items, where the 'smaller' scale will be about 50% of the 'larger' scale, it is still a case of money, preference and availability.
Many people get lessons as part of their art education, teachers usually set the size as well as the subject and medium.
Or at least talk it through with the student to get the best result for the project.

If you are self taught, you will have to experiment as much as your purse allows you.
I find in almost all crafts and arts, I go for smaller once I know how to do the technical side.
Others I have met or know about do go for bigger and huge. 

Each person has to find his/her own way.

About scale influencing the design
Basically the design should be independent of the scale. The smaller you work, the smaller the details should be. The bigger the scale, the more likely you will not put in small details but you will still be able to.

If you look at huge canvasses of old masters, Rembrandt van Rijn for example, you will see that most of the work is wide strokes of the brush or whatever tool they used. There might be some details, but most of those will not stand out when you are at a distance to appreciate the whole of the canvas.

That goes even more when you go for more than lifesize sculpture.
Take as an example the Angel of the North.
The huge statue does not have more details than the man sized marquettes.

Of course you can decide to make a 4 by 3 meter painting with as much detail per cm as miniature paintings, but that is a design decision, not something that comes from the scale used.