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PowerShell Code to deploy solutions (WSP) :-

PowerShell to deploy the WSP to the GAC on server and deploy to all URLS

Add-SPSolution -LiteralPath $path
install-spsolution -Identity $solution  -GACDeployment

PowerShell to deploy the WSP to the GAC on server and deploy only to 1 specific web application (not in bin folder)

Add-SPSolution -LiteralPath $path
install-spsolution -Identity $solution -WebApplication $oURL  -GACDeployment

PowerShell to deploy to specific webapplication at bin folder on server

 Install-SPSolution -Identity $solution -WebApplication $webApp

PowerShell to deploy to all the webapplication at their bin folders on server

Install-SPSolution -Identity $solution -AllWebApplications

When a solution is deployed globally, all SharePoint application pools, including Central Administration’s, are recycled automatically. This can be good and bad. This is good because any GAC installed DLL that has been upgraded needs to be reloaded. This can be bad though with regards to the availability of your entire SharePoint Farm.

When a web application targeted solution is deployed or retracted, only the application pools of the targeted web applications are recycled. When deploying and retracting a web application targeted solution, deploy or retract it only to those web applications that will use it … thus preventing unnecessary recycling of application pools.

When a solution is deployed globally, the assembly DLL file will go and sit under windows\assembly folder. All SharePoint application pools, including Central Administration’s, are recycled automatically. This can be good and bad. This is good because any GAC installed DLL that has been upgraded needs to be reloaded. This can be bad though with regards to the availability of your entire SharePoint Farm.

When a web application targeted solution is deployed or retracted, the assembly DLL file will go and sit under the inetpub\websitename\bin folder. Only the application pools of the targeted web applications are recycled. When deploying and retracting a web application targeted solution, deploy or retract it only to those web applications that will use it … thus preventing unnecessary recycling of application pools.

Reference: Understanding Scope of SharePoint Features