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.