90 day "Introductory Period" in a job offer... Red flag?

Have a job offer with the following clause... Why would a company need to say this? Location: California, in case that matters.

Employment Relationship. The first 90 days of continuous employment with the Company is considered an introductory period. During this time, you will learn your responsibilities and the performance standards expected of you, get acquainted with fellow employees, and become acclimated to your new position. Your supervisor will monitor your performance and may provide a performance review upon conclusion of the introductory period. Successful completion of the introductory period does not make an employee a permanent employee, nor does it entitle you to remain employed by the Company for any definite period of time, but rather allows both you and the Company to evaluate whether or not you are right for the position and whether you are qualified to become a regular employee of the Company. Employment with the Company is for no specific period of time. Your employment with the Company will be “at will,” meaning that either you or the Company may terminate your employment at any time and for any reason, with or without cause or notice. Any contrary representations which may have been made to you are superseded by this offer. This is the full and complete agreement between you and the Company on this term. Although your job duties, title, compensation and benefits, as well as the Company’s personnel policies and procedures, may change from time to time, the “at will” nature of your employment may only be changed in an express written agreement signed by you and the Company’s Chief Executive Officer.

TC 210, YOE 13 #tech