Read through this link
Originally Posted by Paolopd
why you use double quotes?
to gain a understanding of the usage of quotes
As you might know, && means to do command if the previous command suceeds. This means it is a special character that is interepted by the shell.
When it is in single quotes, the shell does not interpert it as a special character and processes it as a normal character.
Double quotes however will make some special characters stay normal and have others stay special.
I used double quotes because I wanted to alias to understand it as a command, but not break as would happen if you did this:
alias uu=sudo aptitude update && sudo safe-upgrade
This would result in uu being set as sudo and then aptitude would run with arguements update (not as sudo) and continue the rest of the command.