Only using tags and variables you need
There are many urls which you don’t need to tag for example if you have an analytics account and it is linked to an active Google Ads account then you wont have to tag your urls destinations if you have auto tagging enabled. If you are running paid ads though you will need to run tags in order to track them effectively. The main variables that you would want to keep track of would be Campaign Source, Campaign Medium, and Campaign Name. Campaign Term.
Using them for your campaign
This would be very helpful for picking out very specific parts of ads you want to check. So say you have very successful ad and se a major increase in traffic but you want to see where all the traffic is coming from. This way you can see whether they are referral or organic searches. Then to get further into it you can see form which referral links are you getting the most traffic so you can help decide where to allocate more resources or funds to that area.