If the television is well-designed, tilting it should not affect its performance. However, there are a couple of cautions. You can never trust the manufacturer to design something so that it can be used in a way that is not intended. Most televisions are intended to be used in an upright or close to upright position. Installing them upside down, for example, could cause a heavy, plug-in component to work loose over time - something that would be impossible to happen if it was upright. A plasma screen is fairly heavy. It is possible that the weight of the screen could cause it to be damaged if it is oriented horizontally for an extended period of time. The weight of the screen would cause it to bend, which could lead to mechanical failures from the unusual stress. However, a television is unlikely to be used in such a position, unless you mount it flat to the ceiling. If this is the case, you should ensure the manufacturer states that it can be used in this position. Plasma monitors are frequently used in industrial applications, where they are installed close to the ceiling and angled forwards or mounted low and angled upwards so that users can view them. The traffic control centre in the city where I live was refitted with plasma monitors a few years ago and they were installed in this fashion.

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No reason for it to be damaged. do you mean putting something under one side of the stand?