Is robots.txt file necessary

[FONT=Georgia]It is not absolutely necessary. But if you want to hide some files or directories from Google robot, you can give instruction in this section. You can create a robot.txt file and then instruct the robot exude them while crawling.

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Robot.txt file is like a gateway of robots once you prevent them from indexing your site then they won't crawl it. But some SE bots don't follow this robot.txt file.

It is not necessary to have robots.txt file because i know one site which don't have robots.txt even it is good on SERPs and index also.

Website will operate without robots.txt file, though there are so many benefits that are attached toit, that you should strongly consider including one.

Robot.txt is not necessary but it has lots of benefit. It includes disallow facility also.
So its better to have robot.txt file on your root directory.

It is not necessary, but you can get benefits from robots.txt so, don't worry about it.

You should use robots for telling search engines stuff.

Ofcourse its not very necessary. Its just the helpful for crawling websites.