Too many folders in the path variable

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http://superuser.com – I've encountered a strange issue - I can't launch Visual Studio, nor run simple commands from command prompt, seemingly due to my PATH variable being too long. Now that I look at it, I see that many companies have added their install directories to the PATH variable. I was wondering why these companies added their folders to the path (perhaps to make it simpler to execute their programs?), and which are necessary and which I can delete. If I delete some of them, will I not be able to launch the programs? (Here's what currently exists in the path) (HowTos)