Each Infinity Gem/Stone possesses an individual "talent." Combining the talents of multiple stones would result in unexpected behaviours. Each stone is also represented by color.
For example: If someone had obtained the Blue MIND Gem/Stone and then used it in combination with. for example the Orange TIME Gem/Stone this could potentially enable the possessor to travel through TIME with only the power of their MIND.
Throw in the Purple "Tesseract"/Cosmic Cube/Space Gem/Stone and you've got a combo that might permit someone to use their MIND to move through both SPACE and TIME.
Also, we've seen that individuals can fall under the control of the Infinity Gem/Stones. Jane Foster was infused with the Red "Aether"/POWER Gem/Stone, and numerous S.H.I.E.L.D. agents fell under Loki's control after being touched with his staff, which appears to contain the Blue MIND Gem/Stone.