Recently I've noticed many large employers have in their career portal the possibility to apply to a "General applicant pool" when postings may not be relevant for a candidate, but where the candidate can assume the employer may have use of them. Say it is an engineering firm, they are looking for juniors, but you are a senior, and you know there is a good chance they will look for seniors two months from now.
My professional profile is quite hybrid; I have a non typical professional path (like returned to school in a field unrelated to the first, both are useful in my industry, just that fields are usually exclusive from one another). Thus I rarely find a job posting requiring both - and consequently I apply to the general applicant pool with the hope that HR will see larger than the boxes (job posting) they create, or that they will just put me in a box somehow. I prepare a targeted cover letter explaining how my hybrid profile may be of interest for this particular firm and join my CV. But I never had a callback for applying in the general candidate pools.
Are general candidate pools used at all? Should one bother with this?