What is the meaning of time alignment timer in SIB1?

Hi, dears.
While I was checking sib1 log, I found there is a timealignmenttimercommon which is set as infinity. If the ue is in idle , has not sent RACH to the BS, then in my opinion, there is no need to have uplink time alignment with the BS. Then why does the BS broadcast a timealignmenttimercommon inside the cell? What is the meaning of this parameter?