All about SandBox Solutions

SandBox Solutions:

• Scope of the solution is Site Collection and not entire farm.
• Deployed and managed by Site Collection Administrators.
• Sandbox solutions are hosted on SharePoint User Code Server Worker Process(SPUCWorkerProcess.exe) where as Farm solutions are hosted on IISWorkerProcess(w3wp.exe)
• Sandbox solutions are uploaded to Solution Gallery(_Catalogs/Solutions).
• No need of IIS reset or IIS App Pool recyclying.
• Used for Web Parts, Event Receivers, Feature Receivers, Custom SharePoint Designer Workflow Activities.
• Sandbox solutions are stored in Content Database not in GAC.
• When a site is restored, it gets Sandbox Solutions also, if any.
• Assemblies in a sandbox solution are included in Solution package(.wsp) and package is deployed to Site Collection 's Solution Gallery.
• When Sandbox solution is accessed(i.e when user navigates to a page that contains web part from Sandbox solution), any assemblies in the solution are extracted from Package in the gallery and copied to the file system(C:\ProgramFiles\Microsoft\SharePoint\UCCache) of the server that is handling the sandbox request.
• For Sandbox solutions coding, referrence the Microsoft.Sharepoint.dll from  the path, ...\14\UserCode\Assemblies. For Form solutions this dll can be  referrenced from ...\14\ISAPI folder.
• To access resources outside a site collection from within Sandbox solution, you must implement and call a Full Trust Sandbox Proxy.

Disadvantages:

• Can't access outside Sandbox(Ex: Database, Registry, Environment Variables)
• Can only access same domain, other domains can't be accessed.
• Can't be used for application pages, visual web parts, code-based workflows, unmanaged code, web service calls, SPUtility.Sendmail, RunWithElevatedPrevilages, Writing to Disk, Accessing objects in other site collection.
• Sandbox solutions by default have code limits to 300 points.
• Microsoft.Sharepoint.WebPartPages not allowed

Powershell Commands:

• To upload Sandbox solution to Site Collection's Solution gallery, 

          ADD -SPUserSolution -LiteralPath .wsp 
                                               -Site

• To Deploy(Activate) SandBox Solution,

          Install -SPUserSolution -Identity .wsp
                                                 -Site 

• To Update  SandBox Solution,

          Update -SPUserSolution -Identity .wsp                                                  -Site 
                                                  -ToSolution .wsp