Firstly I assume clone is being used to mean non IBM PCs.
Advantages:
Cheaper, easier to service, can be faster, can be more easily upgraded. There is more technical support
Disadvantages:
Provided the components are manufactured by reputable companies, and that they are being chosen and assembled by appropriately skilled assemblers ( who are able to match components and assemble them properly) there are no disadvantages
However, there is a danger of purchasing products assembled from low quality components, or by low-skilled self-styled experts or deliberately dishonest dealers. Eg. Using secondhand or substandard parts
Advantages:
Cheaper, easier to service, can be faster, can be more easily upgraded. There is more technical support
Disadvantages:
Provided the components are manufactured by reputable companies, and that they are being chosen and assembled by appropriately skilled assemblers ( who are able to match components and assemble them properly) there are no disadvantages
However, there is a danger of purchasing products assembled from low quality components, or by low-skilled self-styled experts or deliberately dishonest dealers. Eg. Using secondhand or substandard parts