This is not true as the PC has a maximum capacity to which it can perform to
. If you are not able to keep up with that then there system reaches a plateau because of which there would not be any other growth and the system would not be able to perform more than that. Therefore unnecessary increase in the RAM would just lead to growth in the number of RAM capacity, where as it is not essential that the RAM would be lying unutilized in the system, Therefore if your system is capable of handling 1GB of RAM and you have about 4GB RAM in your system then the excess amount is just lying unused. You could choose not to increase the RAM if you do not have requirements for the same. Therefore it is always advised that you should check about your utility in terms of capacity before investing in RAM for your system otherwise you would be just wasting money on the unused RAM content.