What is Solution User Options (.suo) file
The solution user options (.suo) file is a structured storage, or compound, file stored in a binary format. This file is used to store user preference settings, and is created automatically when Visual Studio saves a solution.
Location of .suo file
The .suo file will be saved in the folder where your Solution (.sln) file exists. You might wanted to set true for “Show Hidden Files and Folder” in “Folder Options” as .suo file is default by hidden.
What informations are saved in my .suo file
This file is used by Visual Studio to store user/solution specific information such as Opened Files, Expanded Nodes in the Solution 
Explorer, Opened Tool Windows and its Positions, User Tasks, Breakpoints, Start-up Project, Contents of Watch window, Whether the project is loaded/unloaded etc. The same file is used by Visual Studio Addins (VSPackages) to persist information that are specific to that solution/user.
.suo file and Source Control
Adding user specific information to source control is not a good idea. Most of the code versioning control ignores .suo file by default. If included, the developer, who checks out the latest .suo file, will loose all his personal settings which is stored in the local .suo file.
Visual Studio performance and .suo file
If the size of .suo file is too large then it can affect the performance of Visual Studio. Deleting the .suo file will boost the performance.
Deleting .suo file
Visual Studio creates a new file with the .suo file extension as soon as you open again the solution. But once the file with the .suo file extension is deleted, any of your existing solution user-specific settings will be lost.
Thanks for Information..
Do you have any idea how to save editor window in to .suo file in vapackage ?In which i want to persist editor window between visual studio sessions.
I find taking a base copy of the suo file how you want it and then when VS gets slow and doggy delete the suo and replace it with your nice fast base copy makes everything all good again : )
It has a hidden file attribute applied. Changing the folder options to ‘Show Hidden Files and Folder’ revealed the SUO file adjacent to the solution file .
When you open a Visual Studio Solution file, i.e. MySolution.sln, a corresponding MySolution.suo file is generated. This file is constantly updated with the current state of Visual Studio (i.e. which windows you have open). When you close and reopen Visual Studio, the previous state is reloaded from this file.
Unfortunately from time to time this can lead to problems. For example, It is common for Visual Studio to crash when too many designer files are opened simultaneously. Because the state is remembered in the SUO file ; it can then become impossible to re-open the Visual Studio solution because it will result in a re-occurring crash. When this occurs I usually just delete the SUO file; and Visual Studio will re-open a solution afresh; without any retained state.
However in Visual Studio 11 Beta I could not find the SUO file? Its normally would be found in the directory adjacent the solution file; yet I could not see it. I ran a search for SUO files on my C: drive and found none.
Thoroughly confused I opened ProcMon.exe and watched what files Visual Studio was loading as I opened my solution. A quick search found the suo file where I had expected it; adjacent to the solution. However the file had a hidden attribute applied to it so I couldn’t see it with the default folder options in Windows 8.
https://office-settup.com/
Changing the folder options to ‘Show Hidden Files and Folder’ revealed the SUO file.