As an IT reservist, will I be passed up on orders for only being TS eligible and not having an active clearance?

I am thinking of joining the reserves as an IT. I was recently informed that if I do I won't be granted a TS clearance unless I am assigned to a billet requiring it, only clearance eligibility.

If I don't have an active clearance does this mean I won't be able to take orders listed on zipsurve as requiring TS clearance? Or will they give me an equal opportunity to be selected and make my clearance active?

If any IT reservists could chime in it would be greatly appreciated.