A clearance is essentially a measure of your loyalty to the United States and willingness to protect whatever classified material you receive access to.
Access to classified material requires two things: a clearance to the appropriate level and a 'need to know'. Just because you have a TS clearance it doesn't mean you automatically have access to TS material.
Your 'need to know' is driven by your job. As your job changes, your 'need to know' changes and hence, your access changes.
I had a TS collateral clearance for 40 years and a TS/SCI clearance for 30 years. I am currently out of scope which is fine with me, I'm retired. Others can do their time on the pointy end of the spear.
"Ceterum censeo Islam esse delendam."
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
And Kuchner had an ITEREM TS/SCI