The phrase "are mainly needed" is correct and usable in written English.
It can be used when discussing the primary requirements or necessities for a particular situation or context.
Example: "In this project, resources are mainly needed to ensure timely completion and quality results."
Alternatives: "are primarily required" or "are chiefly necessary."
Lifeboats are few because they are mainly needed to rescue passengers who fall overboard.
Medical fibres are mainly needed because the individual has lost the ability to consume enough of fresh fruits and vegetables.
The models are mainly needed for predictions outside the parameter space.
However, it is unusual to store meats with vegetables, so precautions are mainly needed when storing mixed animal products.
In eukaryotic cells, the UPR results in the transcriptional upregulation of several molecular chaperones and folding enzymes, which are mainly needed to improve the folding capacity of the ER [ 25].
In fact, additional prognostic biomarkers are mainly needed for such patients, as the vast majority of stage I CRC patients will never relapse after curative surgery while most stage IV CRC patients will die from their disease.
The pumping is mainly needed when the sun is shining.
Hot water supply is mainly needed for the CHHP education center.
It can be assumed that a sufficient pressure is mainly needed for the formation of an intimate contact between the Au/Ti film and the silicon substrate.
Further, interference coordination is mainly needed at street crossings and in the border area between radio access points, whereas the border area is smaller than in a wide area deployment.
In a conventional power system with low shares of volatile RES (vRES), flexibility is mainly needed to respond to fluctuations in demand; but with high shares of vRES, it becomes necessary to manage large and at times rapid fluctuations in supply as well [3].
